Melbourne (AFP) - Rafael Nadal called for more understanding from umpires over time warnings as he fought off a spirited challenge from Japan's Kei Nishikori to reach the quarter-finals of the Australian Open on Monday.
The Spanish world number one won 7-6 (7/3), 7-5, 7-6 (7/3) in three hours 17 minutes and will play rising Bulgarian star Grigor Dimitrov in the last eight on Wednesday.
Nishikori, showing the effects of working with new coach Michael Chang, pressed Nadal all the way and had his chances to take sets off the top seed only lose the big points in the match.
"Kei played a fantastic match. Just a few mistakes in some moments that were tough ones. But he played very aggressive, he went for his shots," Nadal said.
"He came on court with determination to take the ball very early and go for the winners.
"It was just a tough match, a very important win."
Nadal was angered when he was called for an unsettling second time violation in between points by chair umpire Eva Asderaki at deuce while 4-4 at a critical time in the third set, but he regathered his composure to go through on his second tiebreaker.
The 13-time Grand Slam champion did not dispute the 20-second rule in between points at Grand Slams, but rather took issue with the chair umpire's handling of it.
"I don't want to change the rule. I accept that sometimes I was slow. I respect that," he said.
"The negative thing in my opinion is not the warning, but the timing of it. You can choose another moment to do it, not that one.
"She didn't advise me before the second warning that I was still going slow. It's a normal thing, for the referee to help the player a little bit, and say, 'Rafa, you are going too slow.' "
Nadal, who is now on a nine-match winning streak, had to adjust to Nishikori's backhand which took some time away from the Spaniard's on-court positioning.
"It was difficult for me to take position inside the court and I was close to losing every set," he said.
"He is always very quick around the court, but today with his backhand today he was able to take the ball quicker and that's why I was struggling for my position on the court."
Nadal broke Nishikori's serve five times, but lost his own on four occasions and had the more effective serve, winning 76 percent of first serve points.
Nishikori paid for his 22 forehand errors, some on crucial points, among a total error count of 51, while Nadal hit 36 winners.
"It's always tough against him on every surface," Nadal said of Nishikori.
"He's a very complete player. He's very quick. He's able to do the most difficult things by taking the ball early and changing the direction.
Kei is a potential top?10 player. So that's the real thing. It's a great victory for me."