Roger Federer has been knocked out of the Paris Masters, falling to big-serving American John Isner while Novak Djokovic kept his winning streak alive.
Isner won 7-6 (7-3) 3-6 7-6 (7-5) to reach the quarter-finals on Thursday, celebrating his second career win over the Swiss legend.
Federer was shocked to find himself leaving for home without once having dropped his serve as Isner typically won on two tie-breaks, hammering down 27 aces in the process.
The Swiss agreed Isner served superbly on the big points.
"I thought he did very well today when he needed it," Federer said.
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"The breakers, he served great. Those are the ones he needed. Yeah, that was the difference."
Federer, who won his hometown tournament in Basel last weekend, will now switch his focus to London and the ATP World Tour Finals.
Rafael Nadal and Andy Murray also reached the quarter-finals, but in contrasting styles.
World No.1 and defending champion Djokovic went through to the last eight in the final tournament of the ATP's regular season with a 6-3 7-5 victory over Gilles Simon that took his unbeaten run to 19 matches.
It was far from being the world No.1's most commanding performance of late as he struggled with his serve, but it meant he has not dropped a set since the US Open final against Federer in early September.
He has now won 26 sets in a row, taking him past his own previous best of 24 sets which he achieved in early 2014.
The Serb, who has won three of the four grand slam titles and five of the eight Masters 1000 series titles so far contested this year, dropped serve five times against the wily Frenchman, four coming in the second set.
But on each occasion he immediately struck back to prevent Simon from gathering any momentum.
The 10-time major tournament winner said his struggles on serve had been frustrating.
"It wasn't pleasant, but I knew that I have a good return. I was feeling the ball very well from the back of the court," Djokovic said.
Djokovic will next play fifth seed Tomas Berdych of the Czech Republic who eased past an injury-hampered Jo-Wilfried Tsonga 6-3 6-4 for a place in the semi-finals.
Isner will play David Ferrer for a semi-final spot after the Spanish eighth seed outlasted Grigor Dimitrov of Bulgaria 6-7 (4-7) 6-1 6-4.
Nadal saved a match point in the second set tie-breaker against South African Kevin Anderson before prevailing 4-6 7-6 (8-6) 6-2.
He will next take on French Open champion Stan Wawrinka who beat Victor Troicki 6-4 7-5.
In earlier action, British second seed Andy Murray set up a quarter-final clash with Richard Gasquet of France by pounding Belgium's David Goffin 6-1 6-0 in just 53 minutes.
Gasquet's win over Kei Nishikori came when the Japanese star abandoned due to back pain while trailing 7-6 (7-3) 4-1.
