By Julian Linden

NEW YORK (Reuters) - Roger Federer mastered the wild weather and his opponent to storm into the U.S. Open semi-finals on Wednesday and remain on course for another showdown with his great rival Rafa Nadal.

Federer was at his brilliant best as he outclassed Sweden's dual French Open finalist Robin Soderling 6-4 6-4 7-5 to reach the last four at Flushing Meadows for the seventh year in a row in conditions better suited for flying a kite than tennis.

"It's not easy, you know. It's cold, everywhere it's blowing. You feel like it's blowing through your ears and into your eyes," Federer told reporters.

"I used to dislike it so much (but) I'm on the other side now. I was able to turn it around and kind of take enjoyment out of playing in the wind."

Yet to drop a set in the tournament, Federer next plays Serbia's Novak Djokovic in Saturday's men's semi-finals with a final against Spain's Nadal looming large. The U.S. Open is the only grand slam where the pair have not met in the final.

Djokovic also advanced in straight sets, beating Frenchman Gael Monfils 7-6 6-1 6-2, but was unable to produce his best after gale force winds turned the last slam of the season into a lottery.

"These are the worst conditions at this tournament," Djokovic grumbled. "I don't think the crowd enjoyed the tennis too much."

Caroline Wozniacki and Vera Zvonarea steamed into women's semi-finals but were more relieved than excited after being tormented by the elements as much as their rivals.

"This felt like playing in a hurricane," Wozniacki said after beating unseeded Slovakian Dominika Cibulkova 6-2 7-5. "It was just about surviving."

Zvonareva was almost apologetic after her 6-3 7-5 win over Estonia's Kaia Kanepi that was littered with 11 service breaks and 88 unforced errors.

"We both were trying our best out there," the Russian seventh seed protested.


The wind inside Arthur Ashe Stadium was blowing so hard that hitting winners almost became a secondary consideration.

Players were repeatedly having to re-toss after gusts blew the ball out of their reach when they were about to serve. Just landing the ball on the court became an achievement.

It lent itself to some comical moments but for tennis purists, it was a day to forget. The only consolation was that Mother Nature did not claim any victims and the four favorites all won easily.

Federer alone seemed unaffected by the conditions, thumping 18 aces past a bewildered Soderling. The fifth seed ended a run of 12 straight losses to Federer when he beat him at Roland Garros in June but normal service resumed on the hardcourts of New York.

"I've played in such strong winds, I've practiced in such hot conditions. Whatever you throw at me, I can do it," Federer said.

"Obviously if it's snowing and tough, then it gets a bit different (but) I haven't had that yet, so I guess I would freak out when that starts happening."

The acrobatic Monfils provided Djokovic with some worrying moments when he grabbed an early service break but the world number three was able to break back and win the first set tiebreaker before running away with the match.

After a slow start to the tournament, Djokovic is starting to show signs that he is getting back to the form that saw him reach the U.S. Open final in 2007, but has to face Federer next.

The Swiss beat him in the 2007 final and the semi-finals each of the past two years and will be an overwhelming favorite to win again.

"I like playing under the radar sometimes," Djokovic said. "It releases the pressure on myself."

After reaching the final 12 months ago and starting this year's championship as the top seed, Wozniacki automatically forfeited any hope she had of quietly sneaking through.

"I'm really competitive," she said. "I really don't like losing."

Wozniacki's opponent in Friday's women's semi-finals is Zvonareva. The winner will play either the defending champion Kim Clijsters or Venus Williams in Saturday's final.

Zvonareva has been one of the most improved players on the women's tour this year and is Russia's highest-ranked player.

She made her first grand slam final at Wimbledon in July and is through to her first semi-final at Flushing Meadows.

"I guess I'm improving," she said. "I've been playing for a while, but I'm still out there and still working hard."

(Editing by John O'Brien)