Chelsea were given a fright by Slavia Prague in a 4-3 home win on Thursday that saw them to a 5-3 aggregate victory and a place in the semi-finals of the Europa League. Already 1-0 up from the first leg, Chelsea were cruising when they scored three more goals in the first 17 minutes at Stamford Bridge courtesy of Pedro, an own-goal by Simon Deli and Olivier Giroud and were 4-1 ahead on the night at half-time. But facing a rout, the Czech visitors restored their pride with two early second-half goals from Petr Sevcik as they threatened a remarkable comeback. Chelsea, however, held on and the London club will face Eintracht Frankfurt for a place in the final after the German side beat Benfica 2-0 to go through on away goals after that tie ended level at 4-4 after two legs. Relieved Chelsea manager Maurizio Sarri told BT Sport: "We started very badly in the second half but I'm really really happy because we played well in the first 45 minutes and we are in a European semi-final which is very important to us. "We knew very well the match was going to be difficult. They ran a lot and with quality -- lot of metres at high speed." Giroud, meanwhile, was proud of Chelsea's resilience after their stumble, with the 2018 World Cup-winning France forward adding: "4-1 at half time obviously maybe in an unconscious way we dropped the intensity down a little bit and even some technical mistakes but this team never give up, I said it before the game." Sarri made five changes from the team beaten 2-0 by Liverpool in the Premier League on Sunday and put Eden Hazard on the wing with Giroud the Blues' central striker. The Londoners doubled their aggregate lead just five minutes into the second leg of this quarter-final tie thanks to Pedro's neat finish after a one-two with Giroud. Minutes later, Chelsea had another goal. Pedro produced a contender for miss of the season when presented with a tap-in from close range that came back off the post only for the ball to fly into the face of Slavia defender Deli and rebound into the net for a bizarre own-goal. Pedro then turned provider, squaring for Giroud to score his 10th Europa League goal of the season. Chelsea were cruising at 3-0 ahead on aggregate and it seemed Tomas Soucek had done no more than score a consolation goal when he rose unmarked to head in from a corner. Chelsea though were soon three goals ahead again when Pedro bundled the ball in. But Slavia rallied impressively after the interval, with Sevcik's 20-yard shot beating Kepa Arrizabalaga at the Chelsea goalkeeper's near post. And soon afterwards, in the 55th minute, Sevcik produced an even better effort from similar range that flew into the top corner as Slavia's fightback continued. But that was as good as it got for the visitors, with Sevcik scuffing a shot that might have seen him complete what would have been an astonishing hat-trick. Pedro celebrates scoring Chelsea's fourth goal in their 4-3 (5-3 on aggregate) Europa League quarter-final win over Slavia Prague Slavia star: Petr Sevcik (L) in action against Chelsea's Mateo Kovacic<doc-sep>The video will auto-play soon 8 Cancel Get the FREE Mirror Football newsletter by email with the day's key headlines and transfer news Invalid Email Something went wrong, please try again later. Sign up Thank you for subscribing We have more newsletters Show me See our privacy notice Arsenal and Chelsea both booked their spots in the Europa League semi-finals on Thursday night. The Gunners avoided any slip-ups in their second leg in Naples, claiming a 1-0 win on the night to beat Napoli 3-0 on aggregate after Alexandre Lacazette's stunning free-kick. Chelsea made much harder work of their tie with Slavia Prague, but in reality their progression was never in doubt despite shipping in three goals in a 4-3 triumph at Stamford Bridge. They will be joined in the last four by Valencia, who thrashed fellow Spanish side Villarreal 5-1 on aggregate. Eintracht Frankfurt snatched a spot in the semi-finals on away goals after beating Benfica 2-0 at home and drawing 4-4 on aggregate. (Image: Getty Images) The draw for the semi-finals was carried out at the same time as the quarter-final draw, meaning we already know both ties. Arsenal will take on Valencia, with Chelsea facing a showdown with Bundesliga side Frankfurt as they all battle for a spot in the May 29 final in Baku with a chance to secure a Champions League place. The semi-finals will take place on May 2 and May 9, with the competition now hotting up in the latter stages. Video Loading Video Unavailable Click to play Tap to play The video will auto-play soon 8 Cancel Play now (Image: Getty Images) Chelsea and Arsenal are both battling to finish in the Premier League top four, but with one of them likely to miss out the Europa League represents a key opportunity to return to Europe's top table and gain some silverware in the process. There is a real possibility of an all-English Europa League final with both clubs likely to be favourites in their semi-final encounters. Semi-final dates May 2 Frankfurt vs Chelsea Arsenal vs Valencia May 9 Chelsea vs Frankfurt Valencia vs Arsenal<doc-sep>For the first time in 35 years, four English teams will appear in the semi-finals of major European competitions for the same season. Chelsea and Arsenal are into the final four of the Europa League after turning in strong performances in their second leg clashes against Slavia Prague and Napoli respectively this morning. The Gunners won 1-0 in Naples to complete a 3-0 aggregate victory care of Alexandre Lacazette’s stunning free-kick. Stream international football with beIN SPORTS on KAYO. Live coverage from 2018/19 La Liga, Bundesliga, Serie A, Ligue 1, Argentine Super Liga & more. Get your 14 day free trial > Meanwhile, Chelsea got home 4-3 in a thriller at Stamford Bridge, meaning a 5-3 aggregate triumph after a goalfest. They’ll be joined by Valencia and Eintracht Frankfurt in the semi-finals. HERE’S A FULL WRAP OF THE ACTION NAPOLI 0-1 ARSENAL (0-3 ON AGG) Alexandre Lacazette’s free-kick calmed any nerves as a defensively stoic Arsenal beat Napoli 3-0 on aggregate to reach the Europa League semi-finals. Lacazette’s strike, a 25-yard curling effort which caught Alex Meret on the wrong side of his goal, put Arsenal effectively four goals up on their hosts, who did not trouble Petr Cech enough to even hint at mounting an unlikely comeback in Thursday’s quarter-final second-leg tie. On a night when Napoli had let fans into their San Paolo stadium nearly three hours before kick-off, instead of inspiring their team, the partisan atmosphere seemed to intimidate the hosts, who managed only one shot on target before half-time when Jose Callejon was denied by Cech’s legs following a rapid counter. Napoli are out of the Europa League Source: AP After half-time, Meret kept Napoli’s faint hopes alive by denying Pierre-Emerick Aubameyang a seemingly open goal with a stunning save, while Arkadiusz Milik wasted a fine chance, sliding too early to meet Mario Rui’s cross and firing wide when the ball rebounded off his midriff on one of the few occasions Napoli breached an impressive Arsenal backline. Arsenal progress to face Valencia, one of manager Unai Emery’s former sides, in the semi-finals, with the prospect of a first European final in 13 years well within sight. CHELSEA 4-3 SLAVIA PRAGUE (5-3 ON AGG) Pedro scored twice for Chelsea as they beat Slavia Prague 4-3 (5-3 aggregate) in a thrilling game to progress to the Europa League semi-finals. Pedro gave Chelsea an early lead (5) before Simon Deli’s unfortunate own goal extended Chelsea’s advantage (10). Chelsea's Olivier Giroud, the Europa League's top scorer, right, celebrates scoring his side's third goal during Source: AP Olivier Giroud scored Chelsea’s third on the night - and his tenth in the competition this season - with a simple tap-in (17) before Pedro added Chelsea’s fourth (27) - 63 seconds after Slavia captain Tomas Soucek pulled a goal back (26). But Slavia did respond in the second half as two quickfire goals from Petr Sevcik (52 and 54) gave the Czech visitors hope of a comeback. But in the end Chelsea progress through to the semi-finals and will play Frankfurt. EINTRACHT FRANKFURT 2-0 BENFICA (4-4 ON AGG) Eintracht Frankfurt have marched on after getting past Benfica on away goals. Strikes from Filip Kostic and Sebastian Rode got the job done in the second leg, but it wasn’t without controversy with the former appearing to come from an offside position to net the opener. The German side are into the final four! Frankfurt's Sebastian Rode (L) and Marco Russ celebrate Source: AFP VALENCIA 2-0 VILLARREAL (5-1 ON AGG) Valencia’s incredible run of form has continued, romping past their La Liga rivals to nab a place in the semi-finals. Goals from Toni Lato and Dani Parejo were enough to seal victory in their home leg. Valencia's Spanish midfielder Dani Parejo (C) celebrates his goal with teammates Source: AFP MORE TO COME...<doc-sep>Sign up to FREE email alerts from Football London - Chelsea Invalid Email Something went wrong, please try again later. Subscribe Thank you for subscribing We have more newsletters Show me See our privacy notice Chelsea are through to the semi-finals of the Europa League after defeating Slavia Prague 4-3 at Stamford Bridge last night (Thursday). The Blues won 5-3 on aggregate in the quarter-final tie, having won 1-0 in the Czech Republic last week, with four goals in the first 27 minutes of the second leg helping Maurizio Sarri's side to victory. Pedro netted the first and fourth goals for Chelsea, with an own goal from Simon Deli and an Olivier Giroud strike sandwiched in between, along with a goal from Tomas Soucek for the visitors. And although Slavia Prague fought back in the second half, scoring two goals through Petr Sevcik to reduce the deficit to two on aggregate, Sarri's men held on to their advantage to set up a semi-final with Eintracht Frankfurt. Blues boss Maurizio Sarri spoke after the game about his side's poor second half performance and joked that perhaps he should not speak to the players at half time in the future. "At half-time I said that the target was the start with the same application and attention in the second half," Sarri said. "But we didn't do it. I don’t know why. It is not easy to understand. Otherwise we can’t solve the problem very easy, but it is difficult to understand why. "I can try not to go into the dressing room at half-time. I can try. If I can solve the problem like this then I will try." The Blues will now travel to Germany to take on the Bundesliga side on Thursday, May 2, before hosting the German outfit in west London a week later. And here's what the Chelsea players have been saying about going through to the last four of the competition. Keep up to date with the latest news, features and exclusives from football.london via the free football.london app for iPhone and Android . 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Chelsea vs Slavia Prague: Sarri reflects on Europa League win Alexandre Lacazette scored the only goal of the game as Arsenal booked their place in the Europa League semi-finals with a clinical 1-0 win at Napoli. Leading 2-0 from the first leg, Unai Emery's side reserved arguably their best performance of the season for their potentially daunting trip to the San Paolo. Lacazette fired home a 25-yard free-kick in the 36th minute and, although Arkadiusz Milik had earlier had a goal ruled out for offside, the Gunners seldom looked troubled. They will face Valencia, one of Emery's former sides, in the last four after they wrapped up victory in their all-Spanish clash with Villarreal. Leading 3-1 from the away leg, Valencia like the Gunners were always in command as goals from Toni Lato and Daniel Parejo gave them a 5-1 aggregate victory. Chelsea held off a second-half fightback from Slavia Prague to beat the Czech side 4-3 at Stamford Bridge and move into the last four with a 5-3 aggregate win. Maurizio Sarri's men looked set for a comfortable night when Pedro and an own goal from Simon Deli extended their advantage in the opening 10 minutes. Olivier Giroud made it 3-0 on the night in the 17th minute and, when Tomas Soucek struck an apparent consolation, Pedro immediately replied with his second of the night. But, roared on by the visiting supporters, Slavia staged a stirring second-half revival and two goals from Petr Sevcik gave them brief hope of a remarkable comeback. Europa League semi-final dates: When will the ties be played? Trending Eintracht Frankfurt hit back from a two-goal first-leg deficit to sink Benfica on away goals and book a semi-final clash against the Blues. The Bundesliga side began the night trailing 4-2, but dominated the first period and reduced the aggregate deficit when Filip Kostic struck a controversial opener after 36 minutes. Benfica were convinced Kostic had been offside in the build-up to the goal and their coach Bruno Lage was sent to the stands for protesting. Sebastian Rode wiped out the deficit in the 67th minute when he drove a powerful shot past Benfica goalkeeper Odisseas Vlachodimos from the edge of the box. Frankfurt keeper Kevin Trapp produced a brilliant fingertip save to deny Salvio in the 79th minute as Frankfurt held on for a 4-4 aggregate draw which sent them through on away goals. Europa League semi-final dates: Who will go on to reach the final? Arsenal: 'Every game is WINNABLE' says Gunners fan