PARIS -- So unbeatable for so long until the closing days of Grand Slam tournaments, Roger Federer is suddenly accumulating early exits.
"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 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. 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.
In women's action, 2012 champion Maria Sharapova ran off the last nine games to come back and beat No. 19 Samantha Stosur, 3-6, 6-4, 6-0, for a quarterfinal berth against 35th-ranked Garbine Muguruza of Spain, the 20-year-old who stunned Williams last week. No. 18 Eugenie Bouchard of Canada will face No. 14 Carla Suarez Navarro of Spain in another quarterfinal.
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."