Andy Murray recovered from his win in the early hours of Thursday to beat Spanish wildcard Marcel Granollers and reach the Madrid Masters last eight.
The British number one, 27, won 6-2 6-0 victory, having started his second-round match against Philipp Kohlschreiber after midnight.
A "very tired" Murray said he had to "bluff" Granollers.
"If they want to see top players playing the best tennis, don't play at three o'clock in the morning," he said.
"I tried to pump myself as much as possible for this match and bluff him to show I was feeling OK."
Murray broke the Spaniard in the fourth and eighth games of the opening set, before breaking a further three times in the second set.
The number two seed, who won the title in 2008, fought back from 0-40 down on his opponent's serve in the final game to seal victory.
He will now face fifth seed Milos Raonic on Friday after the Canadian defeated Argentina's Leonardo Mayer 6-4 6-3.
"I got through this one fairly quickly," added the Scot, who completed his win in 64 minutes. "Hopefully, I'll play a good match in the quarters."
Earlier, Rafael Nadal remained on course for a third successive Madrid title following a 6-2 6-2 win over unseeded Italian Simone Bolelli.
The Spanish third seed will now face Bulgarian 10th seed Grigor Dimitrov in the quarter-finals.
"Yeah, everything worries me about Dimitrov," Nadal said of the player who defeated eighth-seeded Swiss Stanislas Wawrinka 7-6 (7-5) 3-6 6-3.
"He's a very good player. He serves well, very good forehand. Backhand, too. Slice also."
Sixth-seed Czech Tomas Berdych is also in the last eight after a 7-5 6-2 victory over Frenchman Jo-Wilfried Tsonga.
Berdych will play United States player John Isner, who defeated Roger Federer's conqueror Nick Kyrgios 6-3 6-7 (5-7) 6-4.