LONDON — Andy Murray beat Juan Martin Del Potro 6-3, 3-6, 6-2 Sunday in the opening group match of the season-ending ATP World Tour Finals.

Del Potro was troubled by unforced errors and a bloody nose that required medical treatment after the third game of the first set. He didn't seem bothered, saying he has a history of nosebleeds.

"I have a big nose, that's the problem," the Argentine said. "It's just bleeding, I don't know why."

The win puts Murray a step closer to advancing from the round-robin phase to the semifinals of the lucrative eight-player tournament. Two group matches remain for both players.

"It was a really good start," said Murray, who has a 5-1 record against Del Potro. "Me and Juan haven't played that much since the U.S. Open. I kind of expected a little bit of a scrappy match."

Roger Federer played Fernando Verdasco in the late match in Group A at O2 Arena. On Monday, Rafael Nadal takes on Robin Soderling of Sweden and Novak Djokovic of Serbia faces Nikolay Davydenko of Russia in Group B.

Del Potro double-faulted to set up two match points for Murray, and the Scot converted the second with a backhand winner.

Murray took a 5-0 lead in the first set, but Del Potro eventually found his forehand rhythm and saved six set points spread over four games before Murray finally served out for a one-set lead.

Del Potro then dictated play with his forehand in the second set, taking a 3-0 lead as Murray began having problems with his backhand. The Scot broke back for 3-2 but immediately lost his serve again, causing him to send a ball high into the rafters in frustration. Del Potro clinched the set with a scorching crosscourt forehand.

But Murray dominated the deciding set, breaking Del Potro in the second game en route to a 4-1 lead.

"He's got a big serve, long reach, goes for huge shots," Murray said. "You just have to try and find a way through that. Tactically, I've always been quite good. So I found a way through it today."

Murray finished with 30 winners and 26 unforced errors. Del Potro mixed 38 errors with his 31 winners.

"Against Andy, always the match is very tough," Del Potro said. "We play three sets in every tournament, every match. He was a little lucky, but you need the luck to win. And today it was with him."