Cincinnati:Roger Federer was upset in the third round of the ATP Cincinnati Masters on Thursday, meaning Rafael Nadal can capture the world number one ranking by winning the tournament.
Croatia's Ivo Karlovic defeated Federer 7-6 (8/6), 4-6, 7-6 (5/7) and that means Spaniard Nadal can overtake the Swiss star and top the ATP rankings for the first time with a triumph in Sunday's final.
Nadal, who defeated Federer in an epic Wimbledon final earlier in the month, was set to face Germany's Tommy Haas in a later third-round match.
Federer has owned the top ranking for 235 weeks but could surrender the spot after losing to the big-serving Croatian giant in a match where his service was never broken.
"It's disappointing, losing without getting broken, but it's not the first player it has happened to, especially to a guy like Ivo," Federer said. "He served really well, so it was always going to be a hard match."
"There's always danger in tough matches against Ivo. I knew that from the start."
Federer said he did not care whether or not Nadal won the event to take the top ranking spot from him but was going to focus on the Olympics and US Open.
"So far it's OK," Federer said. "I guess I'll analyze and assess my game after the US Open. For the moment it's just all a blur. I mean, it's so many tournaments in a row, big tournaments in a row, it's hard.
"It's a tough trip we've got up in front of us now, going back to China and coming back to the Open.
"I'm looking forward for the next two tournaments. Those are really the ones that can make this season from a good one to a great one again. I hope I can manage to pull off something in the next couple of weeks."
Federer was using the tournament as a tune-up for the Olympics and the US Open, but the defeat was a setback in a month of setbacks that also saw him make an early exit last week in Canada.
"I don't know what to take out of this match," Federer said. "There's always going to be a nothing match, these type of matches. What are you going to do? I just tried to serve well.
"It wasn't an Olympics or a US Open, so I can live with that."
The match turned on a few points in the tie-breaker, Federer failing to convert when it mattered most.
"Maybe I got a little bit unlucky on a couple but he definitely served well. In the last tiebreaker when I had three chances on second serves I wasn't able to get one when I really needed to be on even terms with him," Federer said.
"I guess that cost me the match, which is hard to accept."
Federer blamed some of his performance on a lack of practice time because of so many major tournaments in a row following the Wimbledon finals run with Nadal.
"He's doing well and I have done well in the past as well," 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 US Open."
Novak Djokovic and Ernests Gulbis set up their second battle in as many months by reaching the quarter-finals.
Third seed Djokovic, riding his best run of form in the steamy American Midwest, swamped his second straight Italian opponent as he crushed Andreas Seppi 6-1, 6-2 a day after beating Simone Bolelli in two tie-breakers.
Serbian Djokovic, 21, and Latvian teenager Gulbis hung out as kids when they attended the tennis academy of Niki Pilic in Munich, with Djokovic always refraining at elaborating on any of their off-court adventures.
Gulbis reproduced his French Open form over luckless James Blake, sending the veteran US seventh seed down to a 6-4, 1-6, 6-3 upset.
"I haven't played against top 10 players so much in my career, so beating one of them gives me more confidence," said the world number 53, who still seeks his first career ATP final.
"I knew that he's a tougher opponent on hard court than he is on clay, so I was a little bit nervous, but as the match went on I played pretty well in the beginning, though I lost my concentration in the second set."