Reigning U.S. Open champion Juan Martin del Potro overcame Spaniard Fernando Verdasco on Tuesday to claim his first win at the ATP World Tour Finals.

Del Potro and Verdasco lost their respective first match in Group A and needed a win to keep alive hopes of entering the semifinals. The 21-year-old del Potro finally grabbed the 6-4, 3-6,7-6(1) victory after nearly two and a half hours.

"I served much better than the other match. I was very focused in the important moments, especially in the tiebreak. And I take my opportunities," said del Potro, who lost to local favorite Andy Murray last Sunday.

World No.8 Verdasco looked doomed after losing his serve in the sixth game of the deciding set, but fought hard to chase back with a revenge in the ninth game. However, the debutant at the season finale surrendered quickly in the tiebreak, only managing to earn one point.

"I played bad. He didn't make mistakes and I did quite a lot. So that's why I lost and he won," Verdasco explained the situation in the tiebreak.

Verdasco, who was edged out by Roger Federer in his opener, believed his chances to qualify for the semifinals are pretty few but thought he had played two good matches.

"I was pretty close both days. The level of my tennis I think was good. I need to be happy for the level I played, but also at the same time I'm said because I lost the matches."

Del Potro will face Federer in his final round-robin match while Verdasco is going to meet Murray.