New York: Kim Clijsters needed all her fighting qualities to keep her US Open defence alive and cap an extraordinary day of titanic struggles at the last grand slam of the season.
Now unbeaten at Flushing Meadows in 19 matches dating back over five years, the Belgian regained her composure when she needed it most to reel off four games in a row and defeat Australia`s Samantha Stosur 6-4, 5-7, 6-3 in an error-prone but absorbing centre court clash.
She now faces Venus Williams in Friday`s semi-finals after the former world number one kept the host nation in the championship with a 7-6, 6-4 win over French Open champion Francesca Schiavone.
The United States` hopes of winning the men`s title were extinguished when Sam Querrey lost a four and a half hour armwrestle with Stanislas Wawrinka 7-6, 6-7, 7-5, 4-6, 6-4, the first of two marathon five-setters.
The Spanish pair of Fernando Verdasco and David Ferrer also slugged it out at the Louis Armstrong Stadium for nearly four and a half hours before Verdasco emerged victorious 5-7, 6-7, 6-3, 6-3, 7-6.
Verdasco, who sealed his victory with a spectacular winner that went round the net post, meets another of his countrymen in the quarter-finals with Rafa Nadal and Feliciano Lopez scheduled to meet in Tuesday`s late night feature.
Wawrinka, who upset Andy Murray in the third round, faces 12th seed Mikhail Youzhny in a quarter-final after the Russian outclassed yet another Spaniard Tommy Robredo 7-5, 6-2, 4-6, 6-4.
Clijsters provided a fairytale ending to last year`s US Open when she returned to the game after taking time out to start a family and won the championship four years after her only previous grand slam success.
The second seed had cruised through her first four matches this year in straight sets but found herself in deep trouble against Stosur when she began struggling with her serve in the swirling wind.
"Every match is just a battle and mentally you just have to try and beat it," Clijsters said.
"I didn`t play a good match but I was still able to win it. Even after the match I was `how did I win this?`"
The Australian, who made the French Open final in June and saved four match points in her fourth round win over Elena Dementieva, led 3-2 in the final set before her own serve failed her and Clijsters won all the remaining four games to seal victory.
"I`m gonna be disappointed about this one," Stosur said. "You can`t break serve and have chance after chance after chance and blow it in a quarter-final."
Williams, promoted to third seed this year after her sister and world number one Serena withdrew with an injury, provided a dazzling display that matched her sparkling pink dress to reach the semis at New York for the eighth time in 12 years.
It has been nine years since she won her second successive title at Flushing Meadows but her form over the past nine days has raised hopes of a third crown on the horizon.
"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."
Verdasco, seeded eighth, looked to be heading to defeat against his Davis Cup team mate, seeded 10th, but managed to turn the match around and ended up collapsing on the court with exhaustion after scrambling to hit the brilliant final winner.
"It was a very tough match and after losing the first two sets it was the best comeback of my career," Verdasco said.
Querrey`s agonising defeat left the United States without a quarter-finalist in the men`s draw for the second year in a row.
"I left it all out there today and I didn`t get to the quarters," said a deflated Querrey.
"I`m bummed, but I did everything I could."