MELBOURNE, Australia -- Top-seeded Roger Federer overcame an awkward start to win 13 straight games and beat Nikolay Davydenko 2-6, 6-3, 6-0, 7-5 to reach the semifinals for a 23rd straight Grand Slam.
Tsonga beat Djokovic 7-6 (8), 6-7 (5), 1-6, 6-3, 6-1 in a near four-hour match and will play Federer in a semifinal Friday. Djokovic appeared to be affected by breathing difficulties and stomach problems during part of the match and took a medical timeout trailing 2-0 in the fourth set.
Djokovic said he had an upset stomach before the match, probably as a result of something he ate.
"I had to go to the toilet otherwise I would have thrown up on court," Djokovic said. "When you lose a lot of fluids, your engines stop working and that's how I felt."
Tsonga said he wasn't sure how much the illness affected Djokovic.
"He had a little bit of a stomach problem," Tsonga said. "It's strange because sometimes he doesn't play the point, and when it starts to become important he plays."
Last year, Djokovic retired in the fourth set of his quarterfinal against Andy Roddick with a heat-related illness, but the weather conditions Wednesday night were cool and breezy.
Federer is impressed with his Grand Slam semifinal streak.
"It's incredible, looking back on how many years that is now, I'm able to deliver at Grand Slam play," Federer said. "For some reason I was just a bit worried I was not going to make it this time in the semis.
"Now obviously that it's safe again and I've been able to add one. Definitely one of the most incredible things I have in my résumé."
Federer's victory snapped a 13-match Davydenko winning streak after the Russian won the season-ending ATP World Finals in November at London and his 20th career title in Doha earlier this month.
"I've played him many times before, and I know he goes through ... some rock-solid phases at times," Federer said. "I just tried to stay positive."
Davydenko, who thumped his first three opponents before
grinding a five-set victory over Fernando Verdasco, was
immaculate early, breaking Federer three times to wrap up the
first set and race to a 3-1 lead in the second.
Having declared the top 10 players were "scared" of him
after winning the season-ending ATP Tour Finals in London,
Davydenko appeared determined to live up to his self-proclaimed
reputation, dictating the play and thumping winners from all
The bravado disappeared quickly, however, when given four
chances to take a two-break lead, the Russian blew them all,
following a double fault with three consecutive unforced
Federer, sensing the momentum shift, pounced.
At the end of a breathtaking half-hour of near faultless
shot-making, the Swiss master emerged a set up with a 2-0
lead in the fourth, while Davydenko was left reeling.
As both players struggled to deal with the dipping sun that
left one side of the court plunged in darkness and the other
brightly lit, Davydenko rallied, firing three crisply hit
winners in a row to save match point and break back to 5-5.
"I was like asking 'why now?' He could have played those at
another time when it wasn't important," said Federer, who was
beaten in last year's final by Rafa Nadal.
The 15-time Grand Slam champion bided his time, however, to
take the break back, then dispatched the Russian with a
thumping serve after setting up match point with an ace.
"Pissed off? What else," Davydenko replied when asked how he felt
about his play during Federer's run of successive games.
"But what else [could I do]? Bad luck. [I'll] go home
tomorrow [and] relax."
Information from The Associated Press and Reuters was used in this report.