Clijsters onto semi-final showdown with Venus

Defending champion Kim Clijsters held off a gritty challenge from fifth-seeded Australian Samantha Stosur, surviving an error-filled three-set battle on Tuesday to reach the semi-finals of the U.S. Open.

With both players struggling to hold serve in tricky winds on Arthur Ashe centre court, the second-seeded Belgian steadied herself at the end to complete a 6-4 5-7 6-3 win that set up a showdown against American Venus Williams.

"This whole 10 days has been really tough to get used to the weather conditions," said Clijsters, referencing the severe heat earlier in the tournament and the gusting winds of late.

"Every match is just a battle and mentally you just have to try and beat it."

Clijsters stopped a string of six successive service breaks at the start of the final set to seize a 4-3 lead before breaking Stosur again and then holding serve to end the match.

The victory was the 19th in a row for Clijsters at Flushing Meadows, including her championship run in 2005. Injury and then a temporary retirement to begin a family kept her away from the tournament until her triumphant return last year.

Williams, like Clijsters a two-time U.S. Open winner, was a straight-sets winner over French Open champion Francesca Schiavone in the day's other women's quarter-final.

French Open finalist Stosur, who saved four match points in defeating Russian Elena Dementieva in the fourth round, rose up again to force a third set, ending the last two games of the second set with forehand volleys to win her first set ever against Clijsters after three previous career defeats.

Stosur held serve to end the set after three successive service breaks in winds that made tosses difficult to manage. Clijsters made eight double faults in the 114-minute match.

The spate of service breaks to start the third set made for nine service breaks in a 10-game span before Clijsters righted the ship.

"I was just able to be a little more aggressive in that third set," the Belgian said. "Although my serve wasn't going as well as I would like it to go, I ended up winning."

Clijsters made 43 unforced errors and Stosur, who was up an early break in each of the sets, committed 36 in the mistake-filled, wind-tossed match.

Rafael Nadal edged closer to a place in his first U.S. Open final after thrashing fellow Spaniard Feliciano Lopez 6-3, 6-4, 6-4 on Tuesday.

The world number one, who would complete the collection of grand slam titles with a victory at Flushing Meadows, had few problems wrapping up his fourth straight-sets win of this year's championship.

The start was delayed due to a backlog of matches and did not finish until early on Wednesday morning, but the result appeared a foregone conclusion from the moment Nadal strolled out to the centre court dressed menacingly in an all-black outfit.

His opponent in Thursday's quarter-finals is another Davis Cup team mate, Fernando Verdasco, who advanced the hard way by wearing down David Ferrer 5-7, 6-7, 6-3, 6-3, 7-6 after almost four and a half hours on court.

Number eight seed Fernando Verdasco pulled off the greatest comeback of his career when he rallied from two sets down to edge David Ferrer 5-7, 6-7, 6-3, 6-3, 7-6 in an all-Spanish fourth-round match.

Verdasco's hopes of reaching the tournament quarter-finals for a second straight year looked incredibly slim as he failed to find his range with his high-risk, heavy-hitting style of play and he duly lost the first two sets.

But a medical timeout for treatment to his right ankle turned the tide of a captivating match and the 26-year-old, immensely popular with the crowd in Louis Armstrong Stadium, unleashed a barrage of winners with his powerful forehand.

He levelled the match but found himself a break down in the fifth against the run of play before turning it around to win the four-hour, 23-minute encounter in a deciding tiebreak.

"It was a very tough match and after losing the first two sets it was the best comeback of my career," said Verdasco, who faces another Spanish showdown in the next round against either Rafa Nadal

Former champion Venus Williams ended the run of French Open champion Francesca Schiavone at the U.S. Open when she beat the flamboyant Italian 7-6, 6-4 in the quarter-finals on Tuesday.

The 30-year-old American, seeded third and champion at Flushing Meadows in 2000 and 2001, had a little too much power for the seventh seed, battling through in one hour 54 minutes to reach the last four for the eighth time.

Both players struggled in the gusty winds that swirled around Flushing Meadows, but Williams said she felt she had deserved her victory.

"I feel like when the stakes were higher I was able to raise my game," Williams said. "She did, too, she played some great points. She's just so feisty that you have to kind of keep her at bay. I was glad I was able to do that."

Schiavone, who became the first Italian woman to win a grand-slam singles title when she won the French Open in June, recovered from 4-2 down to force a tiebreak in the first set.

Both players struggled for consistency in the wind but Schiavone came from 4-0 down in the tiebreak to make it 4-4 before Williams closed it out 7-5.

The American, wearing a sparkling pink dress, then stormed to a 4-1 lead in the second set but the resilient Schiavone managed to break back and get on serve again at 4-3.

The Italian enjoyed plenty of success by feeding short slices to Williams, who made 33 unforced errors.

Williams broke again to lead 5-3 but once more, the Italian broke back, only for Williams to break yet again to clinch her eighth victory in their eight meetings.

Stanislas Wawrinka ensured a first for Switzerland at the U.S. Open on Tuesday when he edged out big-serving American Sam Querrey 7-6, 6-7, 7-5, 4-6, 6-4 to reach the quarter-finals for the first time.

Wawrinka wrapped up a gruelling victory in four hours 28 minutes to join five-times champion Roger Federer in the last eight, the first time Switzerland has ever had two men in the quarter-finals of a grand-slam event.

"It's the first time for me (in the last eight) so for sure I'm happy with that," Wawrinka told reporters. "For Roger, he's always in the quarter-finals, but for me it's my first time so it's something important for my career."

Number 25 seed Wawrinka, who upset fourth seed Andy Murray in the previous round, took to the court with the right thigh that he injured against the Scot heavily wrapped.

But the wrap did not seem to affect his movement at all

Wawrinka will now play Russian 12th seed Mikhail Youzhny for a place in the last four.