Tommy Robredo shocked world number one Novak Djokovic Thursday at the Cincinnati Masters, but Roger Federer avoided an upset against Frenchman Gael Monfils.
Spain's Robredo, seeded 16th in the US Open tune-up, sent top-seeded Djokovic packing 7-6 (8/6), 7-5, the defeat coming a week after the world number one Serb was beaten in the third round at Toronto.
The Wimbledon champion now goes into the US Open, the final Grand Slam of the year which starts on August 25, well short of matches and confidence.
Second-seeded Federer, a five-time Cincinnati champion, held off Monfils 6-4, 4-6, 6-3.
He booked a tough quarterfinal against eighth-seeded Scot Andy Murray, who battled more than two hours against the huge serve of John Isner, finally dispatching the American 6-7 (3/7), 6-4, 7-6 (7/2).
Robredo was thrilled to win only his second match in eight encounters with a world number one player. He beat then-top ranked Lleyton Hewitt at Roland Garros 11 years ago.
"It's amazing to be here playing and to beat the number one, I'm more than happy," said the 32-year-old Robredo, who next faces sixth-seeded compatriot David Ferrer -- a 7-5, 6-0 winner over Mikhail Youzhny.
Australian Open champion Stan Wawrinka, the third seed, rallied to beat Croatian Marin Cilic 3-6, 6-0, 6-1.
He'll play France's Julien Benneteau, who beat Jerzy Janowicz 7-5, 6-1.
Fifth seed Milos Raonic made amends with his 30th ace on match point after earlier double-faulting three times while serving for victory.
The Canadian defeated American Steve Johnson 6-7 (7/9), 6-3, 7-6 (7/4) and next faces Italian 15th seed Fabio Fognini. Fognini beat Lu Yen-Hsun of Taiwan 3-6, 6-3, 6-3.
In women's action in the combined ATP and WTA event, defending champion Serena Williams continued her march through the draw, beating Italian 13th seed Flavia Pennetta 6-2, 6-2.