Roger Federer’s hope of reviving his flagging tennis fortunes under the bright lights of the U.S. Open, where he is a five-time champion, were crushed by a straight-sets loss Monday to a player who had never beaten him in 10 attempts.

Tommy Robredo didn’t have to play the match of his life to hand seventh-seeded Federer a 7-6 (7-3), 6-3, 6-4 defeat. The No. 19 seed simply had to be the steadier man, which was stunningly easy against the man many regard as the greatest ever. Time and again Federer made ghastly errors at critical junctures, sending balls flying well past the baseline and plowing others into the net.

“I kind of feel like I beat myself — without taking any credit from Tommy,” said Federer, who converted just two of 16 break points and committed 43 unforced errors to Robredo’s 23. “I kind of self-destructed, which is very disappointing.”

With the defeat, Federer, 32, failed to reach the quarterfinals of the U.S. Open for the first time since 2003.

It’s also the first time since 2002 that he’ll finish a year without reaching the final of any Grand Slam event.

And it scuttles the prospect of the highly anticipated quarterfinal with his greatest rival, Rafael Nadal, which would have been the first time the Swiss and Spaniard met at the U.S. Open.

While Federer was short-circuiting against Robredo at Louis Armstrong Stadium, Nadal was engaged in a more protracted battle with Philipp Kohlschreiber at Arthur Ashe Stadium. With the 6-7 (7-4), 6-4, 6-3, 6-1 victory, Nadal, who has yet to lose his serve in the tournament, clinched a quarterfinal date with Robredo, against whom he holds a 6-0 record.

It has been a difficult summer for Federer, whose ranking slipped from third to seventh in a calamitous eight-week stretch that started with a second-round defeat at Wimbledon, where he was the seven-time and defending champion.

He switched to a larger racket in hopes of spurring a turnaround, only to fare worse. Two weeks later he abandoned the experiment, saying he wanted to prepare for the U.S Open, the season’s final major, with the equipment he knew best.

But he started poorly against Robredo, 31, and swiftly found himself trailing two sets to none.

The crowd did its best to rally the Swiss player, chanting, “Let’s Go, Roger! Let’s Go, Roger!” But his erratic play continued,

With the Spaniard serving at 1-2 in the third set, Federer had three break points but squandered each one. And as his chances of climbing back into contention dimmed, Federer continued on that dismal trajectory.

“Confidence takes care of all the things you don’t normally think about,” Federer said afterward. “It has been a difficult last three months. My consistency is just not there.”

Earlier Monday, Alison Riske’s career-best performance in a Grand Slam came to an end in the rain. Her bid to reach the quarterfinals was denied by veteran Daniela Hantuchova, 6-3, 5-7, 6-2.

Riske, 23, who grew up in the Pittsburgh suburbs and relocated to College Park to train at the Junior Tennis Champions Center in April, was the only American other than Serena Williams still standing in the tournament.

A wild-card entry who had never won a match in the U.S. Open’s main draw before, she knocked off three players, including 2011 Wimbledon champion Petra Kvitova, to reach the fourth-round showdown with Hantuchova, 30, a former world No. 5.

It was the first time Riske had played in cavernous Arthur Ashe Stadium. And it was so overwhelming, she actually welcomed the deluge that halted play in the second set just after she had broken serve to even the score at 4-4.

On balance, Riske said, the tournament was a terrific experience. Just 171st in the world in June, she climbed to 81st on the eve of the U.S. Open and is sure to climb higher as a result of her showing here.

Asked earlier in the tournament what was behind her surge, Riske cited the move to College Park, where she lives with her coach, Yves Boulais, who joined the JTCC staff in April, and his family.

“I feel like we’re one big family there,” Riske said of the JTCC. “It’s so cool for me because most of the kids there, the players, are juniors. But they are wicked. I play with them every day. They are absolutely awesome. I feel like a lot of future champions will be coming out of there.”