Rafael Nadal finally prevails over Kei Nishikori after three-set slog Melbourne Park time lapse: A day at the Australian Open Rafael Nadal celebrates winning the second set against Kei Nishikori. RAFAEL Nadal has vowed to take less time between points after being irked by umpire Eva Asderaki's strict enforcement of the rules during a torrid fourth-round Australian Open win over Kei Nishikori at Melbourne Park yesterday. Nadal was pushed to the limit by Nishikori in a 7-6 (7-3) 7-5 7-6 (7-3) arm wrestle, and annoyed by two separate warnings from Asderaki for taking longer than the allowed 20secs between points. The reigning French and US Open champion also was warned for receiving coaching as he battled to subdue Nishikori in 3hrs,15mins. The Spaniard spoke briefly with Asderaki at the end of a gruelling contest, clearly irritated by her interpretation of the timing issue. While peeved by the timing of Asderaki's second warning at 4-all (deuce) in the second set, Nadal admits he needs to take less time. "I accept the rules, Sometimes I am wrong," he said. Sometimes I am too slow and I accept that. I respect the decision of the referee even if I am not happy for that, because (it) was not the right moment to do it, in my opinion, before an advise. But she did. I going to try to go quicker for the future. But is important to have people on the chair that really understand the game and people who manage this sport who understand the game, and that's it. The negative thing in my opinion is not the warning. The negative thing is the moment - 4-all, deuce. You can choose another moment to do it (issue a warning), not that one. Another thing is she didn't advise me before the second warning that I was still going slow. The normal thing is (to) say 'Rafa, you are going too slow.' Rafael Nadal in action against Kei Nishikori. So I try to go quicker, before the second warning. But she didn't make it...in my opinion, that goes against the show. The dispute prompted coach and commentator Brad Gilbert to call for the installation of clocks on court to alert players to potential time violations. Nadal is renowned as a player who takes the maximum allowed time between points, but generally responds well to pressure from umpires to speed up. Nadal was relieved to earn a tilt at 22nd seed Grigor Dimitrov, the first Bulgarian male to reach a grand slam quarter-final after a dogged 6-3 3-6 6-2 6-4 triumph over Spain's Roberto Bautista Agut. Rafael Nadal celebrates after beating Kei Nishikori. "It was a very difficult match," Nadal said, referring to Nishikori's challenge. I was close to lose (ok) very set. Kei played very well. He hits the ball very early, which is very difficult, and he does it very easy. The ball was coming back fast. Chasing a second Australian Open crown, Nadal endured a rollercoaster afternoon. Flamboyant Dimitrov follows the famed Maleeva sisters - Manuela, Katerina and Magdaleeva - and Sesil Karatantcheva and Tsvetana Pironkova - as Bulgarian members of the grand slam's last eight club. Now coached by Australian Roger Rasheed, former prodigy Dimitrov is delivering on undisputed talent. A Wimbledon and US Open junior champion, Dimitrov last year hooked up with Rasheed, a no-nonsense figure renowned for demanding physical and mental toughness from his charges. Dimitrov, 22, was elated to reach the quarters, but has designs on going even deeper. "First of all, I'm really happy to be out there in the quarter-final," he said. (But) I'm not even close to satisfaction. I've been working really hard in the past year, especially in the off-season. Whether I like it or not, the patience is one of the main ingredients to become good.