LOS ANGELES (AFP) - Argentine teenager Juan Del Potro won his third straight ATP title by outmuscling Andy Roddick 6-1, 7-6 (7/2) in the final of the Los Angeles Classic.

The 19-year-old who will climb into the ATP top 20 for the first time, has now claimed his last 14 matches.

His streak includes wins on clay in July at Stuttgart and Kitzbuehel before making the successful change to cement.

Roddick fell in a heap, never having a look at the Los Angeles title, the only American summer event that he has never won.

"No question, he played lights-out," said Roddick, who still pronounced his week a success. "I'm not sure I would have been able to handle him in any case today.

"No doubt he has talent and he's been able to keep this up for five or six weeks."

The underdog Del Potro earned his second career win over a top 10 player.

"I only want to keep playing at this level," said the winner, three for three in career finals and all played over the past month.

"This was the best win of my career. I beat Tommy Robredo last year, but this is the ultimate."

Roddick's grand plan to tune up for the US Open starting in a fortnight by skipping the Beijing Olympics stalled at the final hurdle as the top seed and former number one went down in 90 minutes.

"It's been a good week, considering that I was only hitting the ball again a week ago after not being able to move my neck. I'm looking to improve and carry it forward next week in Washington," said the American.

Roddick was treated on court for lower back pain - he later said it was nothing serious - after trailing 1-4 and winning just four points in the first four games.

Del Potro broke three times in the opening set and came through calmly in the second-set tiebreaker to notch the win.

"I played a very good week, and I played unbelievable today," said Del Potro, 23-8 on the season. "I don't think Andy was 100 percent, but it is great to play and win here.

"I can play relaxed with a lot of crowd support. I'm happy with my game and my tournament."