Roddick to take on Del Potro

Del Potro earned a shot at winning his second title of the year by wearing down Chile's Fernando Gonzalez in oppressive afternoon heat 7-6, 6-3 in the other semifinal.

"It will be tough," Roddick said of Sunday's final against Del Potro. "You know what you're going to get from him. He plays at a high level every day. That's why he's sixth in the world."

Roddick, bidding for his fourth Washington title, managed only nine aces but never lost his serve during the two-and-a-half hour match against the 80th-ranked Isner.

Pennetta stuns Sharapova
In Los Angeles, Italy's Flavia Pennetta stunned former world number one Maria Sharapova 6-2, 4-6, 6-3 in the semifinals of the LA Championships on Saturday.

Pennetta, the 10th seed, will meet Samantha Stosur in the final after the Australian used her big serve to overwhelm Romanian teenager Sorana Cirstea 6-3, 6-2.

Playing her eighth match in 12 days, three-times grand slam champion Sharapova clearly lacked energy as the match wore on and squandered a 3-1 lead in the third set thanks to a litany of double faults and sloppy errors. 

"I didn't feel fresh," said Sharapova, who double faulted 16 times and had 61 unforced errors compared to 23 from Pennetta.