Rafael Nadal beat a visually impaired Novak Djokovic 7-5, 6-2 at the season-ending ATP World Tour Finals.

Djokovic called for a time out early in the eighth game because of a problem with his contact lenses. After Nadal held at love to 4-4, Djokovic left the O2 Arena court for a bathroom break to fix the problem, but it appeared to continue to bother him.

A few games after the break, shortly after Nadal broke Djokovic and then held to win the first set, the third-ranked Serb called for a trainer.

With medical personnel looking into both eyes, Djokovic looked frustrated as he sat in his changeover chair. He slammed a bottle of water on the court, and then slapped his hand twice into the arm rest.

When he came back on court, Nadal broke to open the second set, and then again in the third game to take a 4-0 lead.

“Very sorry for Nole (Djokovic) and what happened with the eyes,” Nadal said. “For me it was my best match here in London on this court.”

Nadal, who lost all three of his matches at the O2 last year, was first to earn a break in the first set to take a 3-2 lead, but Djokovic quickly got back on serve by breaking back in the next game. Djokovic had three more break points in the final game of the first set, but each time he failed to keep the ball in play.

Both finished the match with winners, but Djokovic had 31 unforced errors to Nadal’s 15. Nadal will next face Tomas Berdych. The Czech defeated Andy Roddick 7-5, 6-3 in the early Group A match.

The combined results mean that all four players are still in the hunt for a spot in the semifinals. The same is true in Group B, which includes Roger Federer, Andy Murray, Robin Soderling and David Ferrer.

Berdych won his first match at the ATP finals and left Roddick with a 0-2 record. The sixth-ranked Czech converted his first break point in the 11th game of the first set, only minutes after saving two set points from Roddick. It was his first win over the eighth-ranked Roddick in four matches this year.

“I just went there, serve twice pretty good, turn the game,” Berdych said of the saved set points. “The last pickup volley was (a) very tough one, and I made it. And then the next game (I) just made a quick break, and that was the key of the game.”

In the second set, Roddick was annoyed by the advertising lights at the feet of the line judges, which flashed red sometimes while play was going on. Shortly after complaining to the chair umpire, Roddick was broken for the second time, giving Berdych a 3-2 lead.

Roddick smashed a ball high into the rafters in anger, and then broke his racket on his foot, drawing a code violation from the chair umpire.

“The neons in the back weren’t quite to the settled position. They were still advertising fun stuff,” Roddick said. “When you’re trying to track a ball, it’s kind of neon lights and stuff. Then Tomas noticed it. A couple of them just went out before we played a point.”

The match finished with the lights off. Berdych, who is now 1-1 at the round-robin tournament, held serve twice after the incident and then broke Roddick again in the final game.

“Playing Rafa, it’s always great experience, even if you play on clay, grass, indoor, outdoor, whatever,” said Berdych, who lost to Nadal in this year’s Wimbledon final. “He played a really tough match (in) the first one (against Roddick). He was able to come back, won the match. Now he’s waiting for another tough, really tough opponent.”

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