Flushing Meadows, NY (My Sportsbook) - Tall Argentine Juan Martin del Potro reached his first-ever U.S. Open semifinal on Thursday.

The sixth-seeded del Potro came from behind to defeat 16th-seeded fellow 20- year-old and 6-foot-6 counterpart Marin Cilic 4-6, 6-3, 6-2, 6-1. Cilic stunned second-seeded and 2008 U.S. Open runner-up Andy Murray here on Tuesday and this marked his best-ever showing at a major.

Del Potro mounted his Day-11 comeback by breaking Cilic's serve to level the second set at 3-all. The big Argentine broke again for a 5-3 lead and then held to knot the bout at a set apiece.

In the third set, "Delpo" broke to open the stanza and notched yet another break for a 4-1 cushion on his way to another easy set win.

The fourth set was all del Potro, as he raced out to a 5-0 lead before crossing the finish line on his first match point in the seventh game of the stanza when Cilic launched one final forehand wide to give the Argentine his eighth break of the match.

Del Potro wound up winning 17 of the last 20 games in what turned out to be a rout after a tight first set. He moved on in 2 hours, 33 minutes, with the help of 53 unforced errors from Cilic.

The ever-improving del Potro is now 2-0 lifetime against Cilic, with the other win coming at the Aussie Open back in January.

This marks del Potro's second trip into a Grand Slam final four, with the other coming at the French Open, where he succumbed to the great Roger Federer, back in June. He's trying to give Argentina its' first U.S. Open champ since the great Guillermo Vilas turned the trick in 1977.

Del Potro's semifinal opponent on Saturday will be third-seeded Spaniard Rafael Nadal or 11th-seeded Chilean Fernando Gonzalez, with those two stars battling here on Thursday night. The six-time major champion and former world No. 1 Nadal, this year's Australian Open titlist, is 6-3 lifetime versus "Gonzo," including wins in their last five encounters.

The other semi will pit a top-ranked Federer against fourth-seeded Serbian star Novak Djokovic. The reigning Wimbledon, French Open and five-time U.S. Open champion Federer beat Djokovic in the final here two years ago. The 15- time major titlist Federer topped Britain's Murray in last year's title bout at the Billie Jean King USTA National Tennis Center.

The 2009 U.S. Open champion will pocket $1.6 million.