Gael Monfils defeated second-ranked Roger Federer 6-4, 7-6 (5) Thursday to reach the quarterfinals of the Monte Carlo Masters.
It was Monfils's second consecutive win on clay over the 17-time Grand Slam champion after he beat him in straight sets during last year's Davis Cup final.
Federer, who played his first tournament since losing in the Indian Wells final nearly four weeks ago, made too many mistakes in a match featuring some spectacular shots.
After they traded early breaks, the Frenchman took advantage of Federer's forehand errors to break in the ninth game and served out the set on his first occasion.
Federer's charges to the net in a tight second set were loudly cheered by the fans but the Swiss failed to build on a 5-3 lead in the tiebreaker as he lost four consecutive points.
Earlier, Grigor Dimitrov capitalized on Stan Wawrinka's awful display to rout the defending champion 6-1, 6-2.
Wawrinka got off a sluggish start and never found the right balance. He also failed to seize his chances, failing to convert four break points in the sixth game of the second set.
The seventh-seeded Swiss player was hoping to advance deeper at the clay-court Masters tournament following a series of disappointing results on hard court at Indian Wells and Miami.
But he could not follow up his solid opening-round showing, hitting 13 unforced errors as Dimitrov raced to a 4-0 lead. The Bulgarian player fended off Wawrinka's assault in the sixth game and broke for 3-1 in the second set after the former Australian Open champions shanked three forehands.
Dimitrov, who made it to the quarterfinals at the Country Club for the second time, saved two other break points and sealed his win after Wawrinka sailed yet another forehand out of court to drop his serve.
Wawrkinka was booed as he left the court.
Widely regarded as a future star of the game, the 23-year-old Dimitrov had also been struggling in recent weeks, failing to win consecutive matches since his fourth round exit at the Australian Open.
Fourth-seeded Milos Raonic advanced, extending his perfect record over clay-court specialist Tommy Robredo to 4-0 with a 6-3, 3-6, 6-3 win.
''Tommy can be tricky on any surface,'' Raonic said. ''He's been having a great 12 months. I was fortunate to get through that match.
''It's 10 months since I last played on clay and I'm still finding my way, but at least I know my objectives, how to reach my goals. It gives me a little bit of a jump start.''
Up next for Raonic will be either Tomas Berdych or Roberto Bautista Agut .
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