juan-martin-del-potroNEW YORK — Juan Martin del Potro was aching for a second crack at a Grand Slam semifinal, a second chance to prove he has what it takes to win at that stage.

By early Thursday evening, he knew he’d get that opportunity at the U.S. Open, thanks to a wind-swept 4-6, 6-3, 6-2, 6-1 quarterfinal victory over 16th-seeded Marin Cilic of Croatia.

What the sixth-seeded del Potro still did not know by the end of the night, however, as rain washed over Flushing Meadows: The opponent he will have to beat to reach his first Grand Slam final.

That’s because the quarterfinal between six-time major champion Rafael Nadal and 2007 Australian Open runner-up Fernando Gonzalez was postponed by showers during the second set.

The first rain delay, of about 75 minutes, came at 2-2 in the second set, after Nadal won the opening set in a tiebreaker. The second interruption came at about 10:20 p.m., with Nadal holding a 3-2 lead in the second-set tiebreaker.

At midnight, tournament officials suspended play for the night, sending Nadal and Gonzalez home. And leaving del Potro still waiting.

The Nadal-Gonzalez match was scheduled to resume Friday, not before 2 p.m. — following the first women’s semifinal, between Serena Williams and Kim Clijsters, which was to begin at 12:30 p.m.

All of the breaks might have been helpful to Nadal, who called for a trainer after the first set. It appeared Nadal was being checked for a flare-up of a stomach muscle problem that bothered him earlier in the tournament.

“In the first set, it was very, very bad,” Nadal’s uncle and coach, Toni, said in a second-set interview with ESPN2, which was televising the match in the U.S. “Now, it’s a little better. It’s difficult. We must win this set.”

Nadal was going to have to wait to try to do that. Organizers had hoped to conclude the match Thursday, because Friday’s forecast called for more rain.

Several hours earlier, del Potro did a much better job than Cilic of dealing with the conditions, which included swirling winds that reached 20 mph.

They are quite similar: Both are 6-foot-6, both have big serves, both have seemingly unlimited potential. And they were born five days apart in 1988, making them the two youngest players ranked in the top 20.

Cilic began brilliantly on this day, racing to a lead of a set and a break. But he started missing more and more, while del Potro stayed steady enough to claim 17 of the last 20 games.

Del Potro has been thinking about this year’s French Open, where he reached the semifinals and took a 2-1 lead in sets against Roger Federer.

Del Potro let that slip away.

He wasn’t about to have the same thing happen Thursday.

“Well, I learn many things. I was so close to beat him,” del Potro said, recalling that loss to Federer. “I have everything to learn, you know. I want to be a good player in the future.”

He finished with only 24 unforced errors — 29 fewer than Cilic.

“He was not missing,” said Cilic, who upset No. 2 Andy Murray on Tuesday.

“Andy, he doesn’t have as much power as del Potro has,” Cilic said.

In the other men’s semifinal Saturday, No. 1 Federer will face No. 4 Novak Djokovic. Federer beat Djokovic at the U.S. Open in the 2007 final and 2008 semifinals, part of an overall 8-4 head-to-head edge.

But there also is this: Federer has reached the final at 16 of the past 17 Grand Slam tournaments, and the only hiccup in that stretch was a loss to eventual champion Djokovic in the 2008 Australian Open semifinals.

The women’s semifinals are Friday, when defending champion Williams will meet 2005 champion Clijsters, and Caroline Wozniacki faces Yanina Wickmayer in a matchup of 19-year-olds both playing in a Grand Slam semifinal for the first time.

Williams is seeking her fourth U.S. Open title and 12th Grand Slam singles championship overall. She also has a chance to win her 10th women’s doubles title at a major with older sister Venus; they advanced to that final Thursday with a three-set victory.

After teaming with Venus to beat Alisa Kleybanova and Ekaterina Makarova 7-6 (4), 3-6, 6-2, the younger Williams acknowledged what has seemed rather obvious for quite some time: She cares much more about major tournaments than others.

“Absolutely. I really play for the Grand Slams,” she said. “Whenever I’m playing elsewhere, I really try. But for me, the Grand Slams — I give it that extra oomph. It’s where you can leave history and leave a mark, and that’s kind of how I look at it.”