LONDON — Nikolay Davydenko won the first big tournament of his career Sunday, running down just about every ball and using a consistent serve to beat U.S. Open champion Juan Martin del Potro 6-3, 6-4 to win the ATP World Tour Finals.

Davydenko, coming off his semifinal victory over top-ranked Roger Federer, dominated his service games against Del Potro, losing only five points on serve in the first set and eight in the second.

Del Potro had three chances to break Davydenko, but the Russian saved them all to complete a sweep of all three of this year's Grand Slam champions at the season-ending tournament.

"For me it was amazing," Davydenko said. "Coming here as No. 7 and winning the tournament, it was surprising for myself."

Davydenko lost in the final of last year's season-ending tournament for the top eight players in the world, falling to Novak Djokovic in Shanghai.

The Russian finished the match with 25 winners and only 15 unforced errors, while Del Potro had 20 winners and 19 unforced errors at the O2 Arena.

Both players had to contend with a crying baby.

While trailing 4-1 in the first set, Del Potro played one point despite the cries of a baby behind him. The Argentine lost that point, bringing the score to 40-15. He then waited to serve to while the baby was carried out of the arena.

In the second set, it was Davydenko's turn to wait while he was serving to even the score at 3-3. He held his serve after the baby quieted down.

This season, Davydenko struggled early in the year with an injury to his left heel, forcing him to withdraw from the Australian Open. But he returned in April, and later reached the quarterfinals at the French Open.

He won his fourth title of the season at the Shanghai Masters to qualify for the ATP finals. He stretched his record to 5-0 in championship matches in 2009 by beating Del Potro.

In London, Davydenko lost to Djokovic in his opening Group B match, but then beat Australian Open champion Rafael Nadal and French Open finalist Robin Soderling to advance. In the semifinals, he finally got the better of Federer, who had beaten Davydenko in their previous 12 meetings.

Federer won both the French Open and Wimbledon this year and clinched the year-end No. 1 ranking for the fifth time in his career.

"He beat everybody, so he's a worthy champion," Del Potro said of Davydenko.

In the doubles final, Bob and Mike Bryan beat Max Mirnyi and Andy Ram 7-6 (3), 6-3 to win their third season-ending title and claim the year-end No. 1 ranking for the fifth time.