WASHINGTON: Chilean fourth seed Fernando Gonzalez ousted Tommy Haas 7-5, 6-4 on Friday to book a semi-final berth against defending champion Juan Martin Del Potro of Argentina at the ATP Washington Classic.

Gonzalez connected on 18 forehand winners and won 30 of 36 points on his first serve to dispatch the Wimbledon semi-finalist in 83 minutes at the 1.4 million-dollar hardcourt tournament, his first tuneup for the US Open.

Del Potro, the second seed from Argentina, advanced to the semi-finals by walkover when Swedish fifth seed Robin Soderling withdrew with a right elbow injury.

"We were both playing really well at the start," Gonzalez said. "He made two mistakes in the first set and I took advantage. In the third set I was able to keep it going."

Gonzalez is 3-0 against Del Potro in the rivalry between South America's top players, but they have not played each other since the second round of the 2007 Australian Open, when Del Potro retired in the fifth set.

Haas, who fell to 1-3 against Gonzalez, netted a weak forehand to hand the Chilean a break chance in the 11th game of the first set, then slammed his racket to the court.

He got a new one but Gonzalez smacked a passing forehand winner for the break, then held to take the set.

Gonzalez broke Haas to open the second set when the German sent a forehand beyond the baseline, then denied Haas on two break points in the sixth game on his way to winning eight of nine points, including a break for a 5-2 edge.

Haas broke back and held but Gonzalez took advantage of his second chance to serve for the match and finished off the 23rd-ranked German with a forehand smash.

Gonzalez, 29, won his 11th career ATP crown in February at his hometown of Vina del Mar and reached the French Open semi-finals, where he lost to Soderling. He took a month off after Wimbledon due to knee tendinitis.

"I've had a lot of recovery time," he said. "When you change surfaces it's very tough. It was really painful at Wimbledon. It's better for my body to play on clay."

Soderling, a week shy of his 25th birthday, lost to Roger Federer in the French Open final and fourth round at Wimbledon then won his first clay title last month at Bastad.

Del Potro, who turns 21 next month, beat Soderling in the semi-finals at Auckland in January on the way to winning his fifth career title.