Juan Martin Del Potro spoiled Andy Roddick's return to the tour after a month-long hiatus by upsetting the top seed 3-6 7-5 7-6 to win the Washington Classic on Sunday.

The 20-year-old Argentine won the final-set tiebreak 8-6, clinching the 2-½ hour slugfest with a scorching forehand that was ruled good after an appeal.

"It was so difficult," Del Potro said after successfully defending his title.

"When you are so close in the third set, you don't want to lose. I was fighting with everything I had."

Roddick, playing his first tournament since losing to Roger Federer in the Wimbledon final last month, saved a match point on Del Potro's serve at 5-6 in the tiebreaker.

Del Potro, however, aced his next serve and then sealed his second tournament win of the year with a forehand that Roddick challenged, but which the replay showed had just nicked the line.

"I thought it might have been out," said Roddick.

"I asked him when he was standing there (at the net) and he also said he thought it might have been out.

"Imagine his disappointment when it wasn't," he added with a smirk.

"With temperatures hovering around 35 degrees Celsius, Roddick said he believed Del Potro was trying to end points quickly.

"Today was brutal," said Roddick.

"It was hot. I think he might have been feeling it more than I did. He didn't want to get in the long points and was going for broke there at the end."

The 26-year-old Roddick, who spent the last month recovering from a hip injury, said he was pleased with his effort, especially with the US Open on the horizon.

"I'm not far off from where I was toward the end of Wimbledon," he said.

"Coming in after being off for a month you want to find out where your form is at.

"To come in here and beat some players and have a look at winning this week, I feel a lot better about my game now than I did when I first got here."

Pennetta supreme

Italy's Flavia Pennetta outran and outsmarted Australian Samantha Stosur to win the LA Championships with a 6-4 6-3 victory in Sunday's final.

Pennetta stayed strong throughout the contest, while Stosur's game fell apart and she was unable to dictate with the big serve and forehand that had carried her to wins over Ana Ivanovic, Zheng Jie and Sorana Cirstea.

The title was the 27-year-old Pennetta's eighth overall, while Stosur, seeded 13th, had been aiming for her first WTA title.

The Australian finished with 32 unforced errors to only 16 for Pennetta.