NEW YORK — Right from the start, Roger Federer looked very little like, well, Roger Federer.
In the opening game of his fourth-round match at the US Open, the owner of 17 Grand Slam titles 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.
No longer the dominant presence he once was, Federer lost in the round of 16 at Flushing Meadows for the first time in a decade, surprisingly beaten, 7-6 (7-3), 6-3, 6-4, by 19th-seeded Tommy Robredo of Spain Monday night.
‘‘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, whose trophy collection includes five from the US Open.
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, to boot — in late June. That ended Federer’s record run of reaching at least the quarterfinals at 36 consecutive Grand Slam tournaments.
This is the first season since 2002 that Federer did not reach at least one final at any of the four Grand Slam tournaments.
‘‘The story of my life: When I lose, people are shell-shocked to see me play this way,’’ Federer said.
When Federer’s match was ending, second-seeded Rafael 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 (4-7), 6-4, 6-3, 6-1 victory over 22d-seeded Philipp Kohlschreiber.
Nadal, who won the 2010 US 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.
Federer was supposed to face Robredo on that main, 23,000-capacity court, but hours of heavy rain in the afternoon muddled the schedule.
Federer-Robredo was moved from Arthur Ashe to the much smaller Louis Armstrong Stadium, which holds about 10,000 spectators and has a less room separating the playing surface from the stands. Federer last competed in Armstrong in 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.
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 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.’’