(changes dateline, updates with men's and women's quarterfinal results)
Frenchman Richard Gasquet squandered a two-set lead but managed to right the ship in time to upset No. 4 seed David Ferrer of Spain 6-3, 6-1, 4-6, 2-6, 6-3 on Wednesday and advance to the U.S. Open semifinals for the first time.
Gasquet used a strong first serve in the opening set to neutralize Ferrer's outstanding return game, while the Spaniard got in trouble due in large part to a low winning percentage on his first-serve points in the early going.
In the second set, the 27-year-old Frenchman took complete control by striking 15 winners in just seven games, including numerous signature down-the-line blasts with his potent one-handed backhand.
Ferrer lived up to his reputation as a fighter, however, and clawed his way back into the contest with more aggressive play from the baseline, while Gasquet began misfiring more frequently with his backhand.
In the fifth set, Gasquet managed to grab a service break in the sixth game and that proved enough to wrap up the quarterfinal match in three hours and 23 minutes.
The eighth-seeded Frenchman will take on another Spaniard - either world No. 2 Rafael Nadal or 19th-seeded Tommy Robredo - in Saturday's semifinals.
Gasquet, who was a rival of Nadal's in the juniors more than a decade ago, has never defeated the Spaniard in their 10 previous matches on the ATP Tour.
In other action Wednesday, 31-year-old Italian Flavia Pennetta advanced to her first-ever Grand Slam semifinal with a 6-4, 6-1 victory over 30-year-old countrywoman Roberta Vinci. EFE