"I feel like a 20-year-old and the way I'm playing, it's great," the 31-year-old Spaniard, who made it to the semi-finals in 1998, said after his fourth-round victory.

• Images from day 9 | US Open 2007

"When you're the oldest guy in the draw you get a lot of support from the crowd and it's a great feeling to be in the quarters," he added.

The Spanish 17th seed was pushed hard by 19-year-old Gulbis but came through to set up a clash with third seed Novak Djokovic [ Images ] of Serbia or Argentine 23rd seed Juan Monaco.

"These kind of matches, they're the ones that keep me very motivated," said Moya, who went five sets to defeat 23-year-old German Philipp Kohlschreiber in the third round.

"The match I won the other day against Kohlschreiber, it's amazing. You're so happy when you finish that kind of a match."

Moya has enjoyed a resurgence this year.

After finishing 2006 ranked 43rd, the Spaniard is now ranked 17th after reaching the quarter-finals at the French Open [ Images ] and winning his 20th career Tour title at the Croatian Open.

The 1998 French Open champion, runner-up at the Australian Open [ Images ] 10 years ago, said he was having too much fun to consider retirement.

"I have never been close to retiring, to be honest," Moya said. "People were asking me, but I didn't feel that it was my time yet. Probably if this year was like the last couple of years, maybe you start thinking about it.

"If I stay healthy, if I'm playing at this level, I can't find a reason to retire. I'm enjoying it as I never did before."