This year, she’ll only play one, though this could be an even more effective version of Venus Williams than the one that came to Flushing Meadows in 2009.

Clijsters and Williams each won their quarterfinal matches Tuesday to set up a marquee semifinal — the No. 2 seed, Clijsters, vs. the No. 3 seed, Williams, and a pair of women both seeking a third US Open championship.

“Just the ability to compete,” Williams said when asked to describe her opponent. “I think in coming back from her layoff, I think she never lost that. Obviously she’s a very good athlete. When you’re a really, really incredible athlete, it really takes your game to another level.”

Last year, Clijsters returned from a 2 1/2 -year layoff and was hoping to use the US Open as a bit of a tune-up and a test — so she could see how big-time competition felt before she made the comeback in earnest in 2010.

In one of the best comeback stories of the year, she ended up winning the whole thing. It started looking like a real possibility when Clijsters beat Williams, who was visibly hobbling on an injured knee, 6-0, 0-6, 6-4 in the fourth round.

In last year’s semifinals, a match remembered for a certain foot fault, Clijsters topped Serena Williams.

Serena isn’t here this year because of an injury. Venus hurt her knee again, too, but recovered in time to play.

“This is probably some of the best of Venus that I’ve seen for a while,” Clijsters said.

Maybe not the cleanest tennis, but certainly good enough to win. Williams overcame nine double-faults and a total of 33 unforced errors — much of it caused by a wind that whipped around Arthur Ashe Stadium for yet another day — to beat reigning French Open champion Francesca Schiavone 7-6 (5), 6-4.

“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.”

Clijsters also got pushed — by No. 5 Sam Stosur. In a match that featured 15 breaks of serve, Clijsters finally held at the end of the third set for a 6-4, 5-7, 6-3 victory. It was one of the few times since the Belgian returned to Flushing Meadows — the 0-6 set last year against Venus was another — when she didn’t appear totally in control.

In men’s play Tuesday — “Spain Day” — No. 1 Rafael Nadal advanced with another three-set victory, this time over fellow Spaniard Feliciano Lopez. Nadal, who hasn’t lost a set or a service game yet in the tournament, advanced to play No. 8 Fernando Verdasco, who defeated No. 10 David Ferrer, also of Spain, in a classic match, 5-7, 6-7 (8), 6-3, 6-3, 7-6 (4).

Nadal-Verdasco will be the first all-Spanish quarterfinal in US Open history. It’s a rematch of their five-setter in the semifinals of the 2009 Australian Open. Nadal won that and is 10-0 lifetime against his Spanish rival.

“He’s playing very good tennis, so it’s going to be a very interesting match,” Nadal said. “I have to play aggressive, to play well. It not going to be impossible, I think.”

Another quarterfinal will pit No. 12 Mikhail Youzhny against No. 25 Stanislas Wawrinka.

Wawrinka beat No. 20 Sam Querrey, which means no American man will be in the quarterfinals at the US Open for the second straight year. More bad news on the US scene: This is the worst Grand Slam year ever for the men, with Andy Roddick making the lone quarterfinal appearance of any American man, at the Australian Open in January. Since the French Open began admitting foreigners in 1925, US men have made at least two quarterfinal Grand Slam appearances every year until now.

“I didn’t feel any extra pressure or anything. I definitely wanted to win and keep the American men (in) — keep the hope going,” Querrey said. “You know, I was close.”