NEW YORK: Juan Martin del Potro reached the US Open semi-finals on Thursday and then sat back and watched as the Rafael Nadal-Fernando Gonzalez match was suspended in the third set due to rain.

The sixth-seeded Argentinian converted eight out of eight break points to reach the last four with a 4-6, 6-3, 6-2, 6-1 win over Marin Cilic of Croatia. In a battle between two giant 20-year-olds, sixth-seeded Del Potro started slowly before wresting control of the match away from Cilic midway through the second set. He finished with a flourish to reach his second Grand Slam semi-final of the year after his five-set loss to Roger Federer in he French Open in June.

Del Potro has enjoyed a meteoric rise through the ranks ever since he emerged in 2006 from the tennis centre of Tandil, which also produced Mariano Zabaleta and Juan Monaco. He was the youngest player in the year-end top 200 in 2005, the youngest in the top 100 in 2006, the youngest in the top 50 in 2007 and the youngest in the top 10 in 2008.

This year, he broke into the top five in April and was ranked there for three months before slipping out to his current sixth ranking. Del Potro enjoyed a good summer buildup to Flushing Meadows, winning in Washington and reaching the final in the Montreal Masters before running out of steam in the final against Andy Murray. But he came into New York well-rested, having taken the next two weeks off and ready for what he has designated as his main target of the year.

Del Potro, though, will have to wait a while longer to find out who his semi-final opponent will be after the first rain of the fortnight forced the suspension of the day's second semi-final with Nadal leading 7-6 (7/4), 6-6 and 3-2 in the tie-break, Gonzalez serving. The Spaniard, though, was in some difficulty with a abdominal strain that had him wincing at times on court and calling for a medical timeout.

Nadal had the same injury problem in his bruising fourth-round match against Frenchman Gael Monfils and there will be serious doubts over whether he can go the full distance at Flushing Meadows. The match was rescheduled for Friday along with the women's semi-finals, but with heavy rain forcast in the New York area for most of the day, organisers could be facing a major scheduling headache for the weekend. Already last year, the men's singles final between Federer and Andy Murray was played a day late on Monday.

The other semi-final was already decided on Wednesday with top seed and defending champion Federer setting up another match with Serbia's Novak Djokovic whom he defeated in the 2007 final and in last year's semi-finals. Meanwhile, unseeded Carly Gullikson and Travis Parrott of the United States won the mixed doubles title by defeating second seeds Carla Black of Zimbabwe and Leander Paes of India 6-2, 6-4.