After suffering back-to-back Premier League losses to top-four rivals Liverpool and Arsenal, Antonio Conte switched to and debuted a 3–4–3 formation against Hull City on the 1 October which earned him a 2–0 victory, thanks to a goal apiece from Willian and Diego Costa.
The new formation featured a back-three pairing of Gary Cahill, David Luiz and César Azpilicueta, with two wing-backs providing cover in the form of Marcos Alonso on the left-hand side and Victor Moses on the right-hand side.

On 15 October, Chelsea earned a 3–0 home victory over reigning Premier League champions Leicester.
The hosts put in a domineering performance against the champions, with Diego Costa opening the scoring for Chelsea in the seventh minute.
Two further goals followed from Eden Hazard and Victor Moses to inflict Leicester's fourth consecutive away league defeat.
Leicester could have potentially pegged a goal back following David Luiz hitting his own goalpost as a result of himself attempting to clear a Leicester corner, however it would merely have been a consolation as Chelsea comfortably claimed another three points.

On 23 October, Chelsea stunned Manchester United and former manager José Mourinho at Stamford Bridge with a thumping 4–0 win.
Chelsea went into the lead within 30 seconds of the match, thanks to Spanish winger Pedro capitalizing on poor defending with a goal.
Gary Cahill smashed in the second after United allowed Eden Hazard's corner to bounce into their box.
United offered little sign of making a comeback, falling further behind when Hazard drilled in a precise 15-yard strike.
The game was well and truly over with a rare 70th-minute goal from N'Golo Kanté compounding Mourinho's misery on his return to Stamford Bridge.
With this win, Chelsea had gone eight league games, winning four and drawing four, without losing against Manchester United, making it their best run against the Red Devils in club history.

Chelsea lost their next game, an EFL Cup game, 2–1 against West Ham at the newly renovated Olympic Stadium on 26 October 2016, knocking them out of the competition.
The game was marred by crowd disturbances amongst both sets of rival fans, with plastic bottles, coins and seats being thrown across the London Stadium.
Prior to the match, there had been nine arrests outside the stadium and 23 banning orders issued by West Ham for disorderly fan behaviour since moving into their new stadium.

Chelsea bounced back with a 2–0 win in the Premier League over Southampton at St Mary's Stadium on 30 October.
The win meant Chelsea won all their Premier League matches in the month of October; a run of four wins, scoring 11 goals without conceding any.
The last time Chelsea had a four-game winning run was April 2015 and the four consecutive clean sheets were also the first since August 2010 when Chelsea had a run of six consecutive Premier League games without conceding.

Source:
After suffering back-to-back Premier League losses to top-four rivals Liverpool and Arsenal, Antonio Conte switched to and debuted a 3–4–3 formation against Hull City on the 1 October which earned him a 2–0 victory, thanks to a goal apiece from Willian and Diego Costa. The new formation featured a back-three pairing of Gary Cahill, David Luiz and César Azpilicueta, with two wing-backs providing cover in the form of Marcos Alonso on the left-hand side and Victor Moses on the right-hand side.
On 15 October, Chelsea earned a 3–0 home victory over reigning Premier League champions Leicester. The hosts put in a domineering performance against the champions, with Diego Costa opening the scoring for Chelsea in the seventh minute. Two further goals followed from Eden Hazard and Victor Moses to inflict Leicester's fourth consecutive away league defeat. Leicester could have potentially pegged a goal back following David Luiz hitting his own goalpost as a result of himself attempting to clear a Leicester corner, however it would merely have been a consolation as Chelsea comfortably claimed another three points.
On 23 October, Chelsea stunned Manchester United and former manager José Mourinho at Stamford Bridge with a thumping 4–0 win. Chelsea went into the lead within 30 seconds of the match, thanks to Spanish winger Pedro capitalizing on poor defending with a goal. Gary Cahill smashed in the second after United allowed Eden Hazard's corner to bounce into their box. United offered little sign of making a comeback, falling further behind when Hazard drilled in a precise 15-yard strike. The game was well and truly over with a rare 70th-minute goal from N'Golo Kanté compounding Mourinho's misery on his return to Stamford Bridge. With this win, Chelsea had gone eight league games, winning four and drawing four, without losing against Manchester United, making it their best run against the Red Devils in club history.
Chelsea lost their next game, an EFL Cup game, 2–1 against West Ham at the newly renovated Olympic Stadium on 26 October 2016, knocking them out of the competition. The game was marred by crowd disturbances amongst both sets of rival fans, with plastic bottles, coins and seats being thrown across the London Stadium. Prior to the match, there had been nine arrests outside the stadium and 23 banning orders issued by West Ham for disorderly fan behaviour since moving into their new stadium.
Chelsea bounced back with a 2–0 win in the Premier League over Southampton at St Mary's Stadium on 30 October. The win meant Chelsea won all their Premier League matches in the month of October; a run of four wins, scoring 11 goals without conceding any. The last time Chelsea had a four-game winning run was April 2015 and the four consecutive clean sheets were also the first since August 2010 when Chelsea had a run of six consecutive Premier League games without conceding.
Source:
2016–17 Chelsea F.C. season