MASON, Ohio -- Roger Federer lost another match and, perhaps, his longtime grip on No. 1, as well.
The world's top-ranked player had another out-of-character setback on Thursday, a 7-6 (8), 4-6, 7-6 (7) loss to Ivo Karlovic that left the Croat exulting on his back and opened the way for Rafael Nadal to take over the No. 1 spot by winning the Cincinnati Masters.
Nadal stayed on course for the seismic shift by beating Tommy Haas 6-4, 7-6 (0) later Thursday, reaching the quarterfinals with his 31st consecutive win. Three more wins and the top spot in the world rankings belongs to him next week.
Even if he doesn't win the championship in Cincinnati, he can pile up enough points to overtake Federer in the next few weeks.
"I know I'm in good position," Nadal said. "In truth, I don't think about it too much."
It's been a long time coming.
Federer has been ranked No. 1 since Feb. 2, 2004, a record 235 consecutive weeks. He and Nadal have held the top two spots since July 25, 2005. They will swap if Nadal extends his run of five consecutive tournament titles.
Asked about the possibility, Federer said, "I don't care."
He's got bigger concerns.
Since his epic five-set loss to Nadal at Wimbledon, Federer has lost in the second round in Toronto and failed to make the quarterfinals in Cincinnati, where he won the title last year. The 26-year-old Swiss star has been struggling to regain his aura of domination since he started the year with mononucleosis.
Nadal has taken advantage by improving his hard-court game and surpassing Federer on the court if not in the rankings.
"Look, he's doing well and I have done well in the past," Federer said. "This year was hard, I guess, with the start of the year. But nevertheless, I still think it's been a good year. I just hope I can show it now at the Olympics and the U.S. Open.
"I'm looking forward for the next two tournaments," he said. "Those are really the ones that can make this season from a good one to a great one again."
There was nothing great about his few days in Cincinnati.
Federer needed three sets to get through his first match. Then he lost for the first time in his career when he didn't drop a game on his serve. He simply couldn't crack Karlovic's tough serve.
Federer had won the six previous times he faced the 6-foot-10 Karlovic, but their matches were close. Federer had won 13 of those 15 sets, although nine ended in tiebreaks.
Appropriately, two of their three sets on Thursday ended in breakers, as well. Using his overpowering serve, Karlovic got the best of them both.
He started the decisive one with a pair of aces -- he had 21 overall in the match -- and went up 6-3 with a 140 mph serve that Federer couldn't return. After Karlovic let a couple match points slip away, Federer hit a backhand long, ending the match.
Karlovic fell on his back and raised his arms in triumph over a win that didn't totally surprise him.
"I already played against him six times and it was always close, so I knew that I'm going to have a chance today," Karlovic said.
Earlier, a 19-year-old Latvian who tends to lose concentration during matches and is getting over a soccer injury -- one of those teen moments -- upset the last remaining American in the draw. Ernests Gulbis took advantage of James Blake's erratic serve for a 6-4, 1-6, 6-3 victory, leaving the United States shut out of the quarterfinals for the first time in the tournament's history.
"Yeah, it's unfortunate," Blake said. "I don't think American tennis is troubled by any means. But the way it is right now, the best players in the world are from Switzerland and Spain."
The 28-year-old Blake got bounced by a player so inexperienced that he still loses focus on the court and can't keep himself away from the soccer field. He sprained an ankle while playing soccer with friends this summer, forcing him to miss a couple weeks on the tour, and was totally out of sync last week while losing in the first round in Toronto.
Given his predicament, Gulbis didn't expect much.
"To be honest, I didn't think that it would happen in this tournament because last week I played really bad," he said. "And I was injured before, so I didn't do nothing basically for two weeks."
He had one thing working for him: Gulbis beat Blake to reach the quarterfinals at the French Open, his best showing in a Grand Slam event. Gulbis came in confident and took advantage of Blake's errant first serve -- only 45 percent were in.
"It's tough to beat a guy like that with a second serve," Blake said. "He's got a ton of talent."
Third-seeded Novak Djokovic also advanced to the quarterfinals, beating Andreas Seppi 6-1, 6-2 to set up a rematch with Gulbis. Djokovic beat the Latvian in three close sets during the quarterfinals of the French Open.