NEW YORK — It's as though Rafael Nadal never left.
If anything, he's playing better than ever.
A year after skipping the U.S. Open because of a bad knee, Nadal powered his way back to the semifinals, overwhelming 19th-seeded Tommy Robredo 6-0, 6-2, 6-2 Wednesday night.
"I think I played my best match at the U.S. Open this year. Great to be able to play your best match in the quarterfinals," Nadal said. "Playing a little better every day is a great feeling."
Nadal, seeded second, improved to 20-0 on hardcourts in 2013, part of an overall record of 58-3 with nine titles, including his record eighth championship at the French Open in June. At the next Grand Slam tournament, though, Nadal flopped, exiting in the first round at Wimbledon.
That surprising defeat, against a player ranked 135th, came on June 24. Nadal hasn't lost a match to anyone since.
In the semis, Nadal faces No. 8 Richard Gasquet, who edged No. 4 David Ferrer 6-3, 6-1, 4-6, 2-6, 6-3. That one took nearly 31/2 hours and was filled with plenty of ebbs and flows, allowing Gasquet to reach his first major semifinal in six years.
Nadal, meanwhile, was never challenged by fellow Spaniard Robredo, who was coming off a fourth-round upset of Roger Federer.
"(Nadal) was up very quick," said Robredo, who is 0-7 in Grand Slam quarterfinals, "and then there was nothing else to do. He was too good."
Gasquet, 27, made his second Grand Slam semifinal, the other coming at Wimbledon in 2007.
"It's a big match for me, a big victory," Gasquet said. "I'm 27. The last time I (reached a major semi), I was 21. It means a lot to me."
Nadal has won all 10 of his meetings with Gasquet on the pro circuit.
"The last time I beat (Nadal), I was 13 years old," Gasquet said. "I've beaten him one time in my life."
When Nadal was asked about that, he smiled broadly.
"Yeah, I think I lost 6-4 in the third," Nadal said. "Yeah, I remember."
Flavia Pennetta, who missed the 2012 Open because of right wrist surgery, reached her first Grand Slam semifinal with a 6-4, 6-1 victory over 10th-seeded Roberta Vinci.
Pennetta plays No. 2 Victoria Azarenka, who beat 48th-ranked Daniela Hantuchova 6-2, 6-3 in their quarterfinal. Azarenka reached her sixth semifinal in the past eight Grand Slam tournaments. She was the runnerup to Serena Williams at the U.S. Open last year.
Williams, the top seed, and No. 5 Li Na won Tuesday to secure spots in the other semifinal on Friday.
Pennetta, 31, spoke after her match about sitting at her parents' place in Italy last year, watching on TV as the Open went on without her. She was asked whether at the time she could have imagined playing at this level 12 months later.
"I hoped so. It's what I hoped for at the start of this year, to be honest. It didn't happen as easily or as quickly as I'd hoped," she said. "But I definitely hoped."
Vinci is a longtime friend and former doubles partner of Pennetta. The Italians know each other's games, and each other's personalities, perfectly. While Pennetta was laid up after her operation last September, they spoke on the phone and sent text messages back and forth.
"She went through some ugly times," said Vinci, who lost in last year's Open quarterfinals to yet another Italian, her current doubles partner, Sara Errani.
"But Flavia is strong-headed. She's stubborn," Vinci continued, rapping a wooden table with her right fist. "She's someone who, when she wants something, she wants it all costs, which is the right way to be."
Williams sisters in doubles quarters: Venus and Serena Williams overcame two service breaks in the second set to advance to the doubles quarterfinals with a 6-1, 7-6 (7-3) victory over Anastasia Pavlyuchenkova and Lucie Safarova. The sisters, who have combined for 13 Grand Slam doubles titles, next play defending champions and top seeds Errani and Vinci. The Italians beat the sisters in three sets in the Australian Open quarterfinals. "We learned from the match in Australia," Venus said. "We're going to learn from that and go for it (today)."