Federer's streak of nine consecutive quarterfinals at the French Open ended Sunday with a 6-7 (5), 7-6 (3), 6-2, 4-6, 6-3 fourth-round loss to 18th-seeded Ernests Gulbis of Latvia.
"A lot of regrets," Federer said. "I just couldn't kind of figure it out."
The 17-time Grand Slam champion had not left Roland Garros so soon since 2004, when he was beaten in the third round by Gustavo Kuerten.
After that decade-old setback, though, Federer made at least the quarterfinals at a record 36 consecutive major tournaments, a streak that ended with a second-round loss at Wimbledon last year. Federer also put together record Slam runs of 10 finals and 23 semifinals in a row when he was at his dominant best.
Now the 32-year-old Federer has bowed out before the quarterfinals at three of the last four majors.
"I think it was the biggest, probably, win of my career," said Gulbis, who most certainly could have dispensed with the word "probably."
Addressing spectators who sang Federer's first name between points, Gulbis said: "I'm sorry I had to win. I know all of you like Roger."
The fourth-seeded Federer's resume includes the 2009 French Open title, and he was a four-time runner-up in Paris to Rafael Nadal. But Federer was hardly in top form Sunday, making 59 unforced errors and getting broken twice while serving for a set.
That included at 5-3, 40-15 in the second, when Federer sent an overhead right to Gulbis, who whipped a backhand passing winner.
"I was lucky, I have to say," Gulbis said about that point. "I was really lucky."
Said Federer: "Things got tough from then on for, like, a half-hour for me."
He lost the last five points of the second-set tiebreaker, then dropped the third set, too.
Another key moment came when Gulbis left the court with a trainer to take a medical timeout while trailing 5-2 in the fourth. As he walked out, Gulbis motioned to Federer, as if asking for permission to go. When Gulbis returned, some fans jeered and whistled at him, and he pointed to his lower back as if to say, "Hey, I was injured."
At his news conference, Federer alternated between sounding a little perturbed about the lengthy intermission -- and resigned to the idea that what Gulbis did was within the rules.
"In the past, I guess, it's been abused much more than today, but still, what can you tell?" Federer said. "He didn't look hurt in any way. But if you can use it, you know, might as well do it."
Gulbis' strokes had momentarily gone astray before that break, but afterward, the 25-year-old Gulbis once again displayed the big-hitting tennis that had many marking him as a future star when he was a teenager. He won 10 of the next 12 points, punctuating shots with exhales that sounded like growls.
The fifth set was all Gulbis, who hadn't been to the quarterfinals at a major tournament since the 2008 French Open. He's spoken openly about focusing more on enjoying the nightlife than perfecting his craft, and drew attention last week for saying he wouldn't encourage his younger sisters to pursue professional tennis because a woman "needs to think about family, needs to think about kids."
In the concluding set, Gulbis raced to a 3-0 lead, thanks largely to Federer miscues. In the second game, Federer netted backhands and forehands to offer up break points, then pushed a forehand wide to give Gulbis a lead he never relinquished.
After that miss, Federer grabbed a ball and swatted it in anger straight up in the air, a rare sign of exasperation from him.
"He's Roger Federer, but he also gets tight, you know," Gulbis said. "He's probably going to make (that forehand) seven out of 10 (times). Other guys are going to make two out of 10. Mistakes happen."
The result fit with the topsy-turvy nature of this tournament: Both reigning Australian Open champions, No. 3 Stan Wawrinka and No. 2 Li Na, lost in the first round; No. 1 Serena Williams left in the second round.
Gulbis now plays No. 6 Tomas Berdych, who eliminated the last American man, No. 10 John Isner. In another quarterfinal, No. 2 Novak Djokovic will face No. 8 Milos Raonic.
Earlier Sunday, reigning Wimbledon champion Andy Murray and No. 24 Fernando Verdasco set up a fourth-round meeting by finishing off victories in matches suspended Saturday night because of fading light.
Murray found his second wind to finally get the better of Philipp Kohlschreiber of Germany, needing 40 minutes to complete a 3-6, 6-3, 6-3, 4-6, 12-10 win.
"I was cramping yesterday. My muscles were obviously fatigued," Murray said. "I actually woke up [feeling] OK ... the nice thing about this surface, compared with the hard court, is when you have a tough match on the hard courts you wake up the next day and your hips are sore, your knees are sore."
Kohlschreiber missed a chance to break Murray in the 19th game of the decider.
"He came up with some great shots when he was behind in games today," Murray said. "I thought both of us served a little bit better. It was a good finish to the match."
Murray, a two-time Grand Slam champion, crouched down and clenched both fists after hitting a two-handed backhand winner on Kohlschreiber's second serve with the score at 15-40 in the 22nd game.
"Last night was extremely tough for me. I did lot of running,'' Murray said. "Considering the circumstances, today I thought we both played some good points. We both came out probably pretty nervous.''
Murray, the 2012 U.S. Open champion, made light of a disturbed night's sleep of barely five hours.
"I was kind of ready to play at 4 or 5 in the morning," he said. "When you know you have to come back and it's 7-all the next day and every single point counts, basically you need to get off to a big start. You're obviously going to be a bit anxious."
He will get a longer rest before playing Monday against Verdasco, who easily beat 12th-seeded Frenchman Richard Gasquet 6-3, 6-2, 6-3. Murray leads Verdasco 9-1 in their career head-to-heads but they have never met on clay.
The Associated Press contributed to this report.
Federer: 'A Lot Of Regrets'
Roger Federer discusses his fourth-round loss to Ernests Gulbis at the French Open.
Federer Ousted By Gulbis
Patrick McEnroe discusses Roger Federer's fourth-round loss to 18th-seeded Ernests Gulbis 6-7 (5), 7-6 (3), 6-2, 4-6, 6-3.
Murray Survives Kohlschreiber
Darren Cahill breaks down Andy Murray's 3-6, 6-3, 6-3, 4-6, 12-10 win over Philipp Kohlschreiber at the French Open.