New York:Argentina's Juan Martin del Potro converted eight of eight break points to reach the semi-finals of the US Open on Thursday 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 will go on to play the winner of the night match between third seed Rafael Nadal of Spain and Chilean 11th seed Fernando Gonzalez for a place in Sunday's final.
The other semi-final will oppose title-holder and top seed Roger Federer of Switzerland against third-seeded Novak Djokovic of Serbia.
"In a big match like today you are going to feel nervous at the start, but I fought until the final of it," Del Potro said.
"The windy conditions were tough for both players but I stayed so focussed on my serve and I never missed an easy ball.
"I am very happy to be in the semis and want to be in the final but both players will be tough for me."
Cilic, playing in his first Grand Slam quarter-final, grabbed the first break of serve in the fifth game, converting his third break point with a tremendous running forehand whipped down the line for a 3-2 lead.
He held serve three more times to take the set, displaying all the attacking skills that destroyed the tournament's second seed, Britain's Andy Murray, in the quarter-finals.
Cilic broke again to open the second set and he held onto that until the sixth game, when the Croatian served up four straight unforced errors on the forehand side to gift Del Potro his first break of the match.
From 3-3, Del Potro, bidding to become the first South American champion in New York since Guillermo Vilas in 1977, took control of the exchanges, stepping up his own game at a time when Cilic started to fade, especially on his forehand side.
The Argentinian made it five games in a row to level the set score and then won the first two of the second set to take command of the match, outplaying and out-thinking the Croatian.
Del Potro took the third set 6-2 and when he broke Cilic again to open the fourth set, the Croatian looked a beaten man.
Civic, who was inspired as a boy by former Wimbledon champion Goran Ivanisevic, had no answer by this stage to the heavier hitting of the South American, who moved out relentlessly with seven games in a row to take the set 6-0 and the match in 2 hours 33 minutes
It will be the second Grand Slam semi-final of the year for Del Potro, who took Roger Federer to five sets in the last four of the French Open in early June.