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Osama Faisal, Associated Press
Switzerland's Roger Federer returns the ball to Grega Zemlja of Slovenia during the Qatar ATP Open Tennis tournament in Doha, Qatar, on Wednesday Jan. 4, 2012

DOHA, Qatar — Rafael Nadal and Roger Federer eased into the Qatar Open quarterfinals in rare cool and windy conditions in Doha on Wednesday.

Nadal routed German qualifier Denis Gremelmayr 6-2, 6-2, while Federer overwhelmed Slovenia qualifier Grega Zemlja 6-2, 6-3.

Federer won his 19th straight match dating to his U.S. Open semifinal loss to top-ranked Novak Djokovic.

Federer and Nadal were joined by the sixth-ranked Jo-Wilfried Tsonga, who saved two set points in the first set before defeating Flavio Cipolla of Italy 7-6 (8), 6-3.

Nadal will face Mikhail Youzhny of Russia, while Federer will play Andreas Seppi of Italy. Tsonga will face Albert Ramos of Spain.

Also, sixth-seeded Alex Bogomolov Jr. of Russia withdrew from the tournament with a right ankle injury, becoming the first seeded player not to advance.

In the late match, 15th-ranked Gael Monfils of France got past Benjamin Becker 7-5, 4-6, 7-5. He'll play Viktor Troicki of Serbia in the quarterfinals.

Monfils hit his left knee with his racket in the second set, fell to the ground and sought medical attention. He said he had slight pain but expected to play on Thursday.

Nadal, who last month said he had too little time to prepare for the season, came out strong . He broke the 189th-ranked Gremelmayr in the first game of both sets and never was seriously threatened. The match could have been more one-sided but Nadal managed to convert only four of 15 break points.

Nadal said he was starting to get a feel for his heavier racket. He said the variety of shots he unleashed was important if he was to play better in the big matches, especially against Djokovic. He's lost to the Serb in six finals last year, including at the U.S. Open and Wimbledon.

"I'm trying to play aggressive, I'm trying to return a little bit better, because for me the worst thing I did for most of last year was the return, especially the second half of the year," Nadal said. "(I'm) so happy with my returns here and happy how a few things have worked well with the new weight of the racket. I'm starting to have good feelings, so that's really important."

Federer again won his match without dropping a set, happy to get off the court in an hour.

"It can, you know, be tricky when you enter sort of the first tournament of the season and right away you play an incredibly tough three setter, let's say," Federer said. "The body feels that, and that's why I'm happy to be through into the quarterfinals without too much trouble."

After winning the tiebreaker, Tsonga picked up his game in the second set. Effectively deploying an array of drop shots and volleys, Tsonga broke twice for 4-1 and a third time to win the match with an emphatic overhead smash.

Tsonga said his net game was something he hopes to improve this season against the top-five players.

"They all have something different," he said. "I mean, Rafa is running a lot, plays with a lot of spin. Roger takes the ball very early, and Novak, too. Andy Murray, he's an incredible defender, and his passing shots are just amazing.

"So, I try to follow my way, and I think my way is to be really offensive and play with my serve, my forehand, and of course my volley, too. So I just try to improve my volley."

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