Right from the start, Federer looked very little like the player who has won 17 Grand Slam singles titles.
In the opening game of his fourth-round match at the U.S. Open, he got passed at the net twice, sailed a backhand long, then missed two forehands to get broken. In the second game, the man who has spent more weeks ranked No. 1 than anyone else dumped a backhand into the net, then shanked two other backhands several feet wide.
"I kind of self-destructed, which is very disappointing," said Federer, who made 43 unforced errors and managed to convert only 2 of 16 break points. "It was a frustrating performance."
Only the latest in a series. This caps a poor-by-his-standards Grand Slam season for Federer, who has won five U.S. Open titles among his record major haul at the majors.
He exited in the semifinals at the Australian Open in January, the quarterfinals at the French Open in early June, and the second round of Wimbledon - against a player ranked 116th - in late June. That ended Federer's record run of reaching at least the quarterfinals at 36 consecutive Grand Slam tournaments.
Now, thanks to Robredo, Federer has a new, unwanted streak: Two consecutive losses before the quarterfinals at majors.
This is the first season since 2002 that Federer did not reach at least one final at any of the four Grand Slam tournaments. That year also marked the last time Federer was ranked lower than he is now at No. 7.
"The story of my life: When I lose, people are shell-shocked to see me play this way," Federer said.
Heading into Monday, the buzz at the U.S. Open was all about looking ahead to a potential quarterfinal between Federer and his nemesis, Rafael Nadal. Owners of a combined 29 Grand Slam trophies, they have played each other 31 times - including in eight major finals - but never in New York.
Federer's loss means they won't fix that gap in their rivalry this week. When Federer's match was ending, the second-seeded Nadal was just getting started in Arthur Ashe Stadium, and the Spaniard wound up improving to 19-0 on hard courts in 2013 with a 6-7 (4), 6-4, 6-3, 6-1 victory over 22nd-seeded Philipp Kohlschreiber of Germany.
Nadal, who won the 2010 U.S. Open but missed it last year with a left knee injury, erased the only break point he faced against Kohlschreiber and has not lost a service game so far through four matches.
"It was very, very tough conditions out there. Very humid," Nadal said. "I sweat too much tonight."
At age 32, Federer has struggled with a bad back and experimented with a larger racket head. And all along, he's had far more trouble winning matches than he usually does - particularly against the sort of players he barely broke a sweat against at his peak.
That this defeat came against Robredo made it all the more stunning. Not that Robredo is a slouch. He's been ranked as high as No. 5, albeit back in 2006, and this is his seventh trip to the quarterfinals at a major. He made it that far at this year's French Open by doing something no man had done since 1927, winning three matches in a row after dropping the first two sets of each.
But until this match, he'd only taken three sets off Federer in 10 losses. And before Monday, Robredo's record in the fourth round of the U.S. Open was 0-7.
Federer was asked whether Robredo tried anything different this time around.
"No, he didn't. Pretty simple. No surprises," Federer said. "He didn't serve-and-volley or chip-and-charge. He stood back the way he usually does. He kick-served the way he usually does."
Federer originally was supposed to face Robredo on that main, 23,000-capacity court, but hours of heavy rain in the afternoon muddled the schedule, including prompting the tournament to postpone two-time Australian Open champion Victoria Azarenka's match against 2008 French Open champion Ana Ivanovic until Tuesday.
In the three women's matches that were played Monday, No. 10 Roberta Vinci and unseeded Flavia Pennetta set up an all-Italian quarterfinal with victories. Vinci beat 136th-ranked qualifier Camila Giorgi, 6-4, 6-2, while Pennetta defeated No. 21 Simona Halep of Romania 6-2, 7-6 (3).
Azarenka or Ivanovic will wind up facing Daniela Hantuchova of Slovakia, who got past American wild-card entry Alison Riske 6-3, 5-7, 6-2.
In men's action, No. 4 David Ferrer, the runner-up to Nadal at the French Open this year, edged No. 18 Janko Tipsarevic 7-6 (2), 3-6, 7-5, 7-6 (3).
Federer-Robredo was moved from Ashe to much smaller Louis Armstrong Stadium, which holds about 10,000 spectators and where Federer hasn't played since 2006.
He said that was not a factor in Monday's outcome, though. The blame, instead, belonged with his inability to hit his strokes the way he wanted.
Federer was particularly ineffective when he had chances on Robredo's serve. Time and again, Federer would get an opening, a chance to begin the long climb back into the match. And he kept letting those opportunities slip by.
Soaked with perspiration, Federer flubbed a backhand to waste one of five break points he had in the fourth game of what turned out to be the last set. He kicked the offending ball, a rare sign of frustration from the generally unflappable Federer.
"I've definitely got to go back to work and come back stronger. Get rid of this loss now as quick as I can, forget about it, because that's not how I want to play from here on," Federer said. "I want to play better. I know I can."