The top-ranked Spaniard goes through as the Group A winner and will meet No. 5 Andy Murray, while Berdych is eliminated.

Trailing 6-5 in the first set, Nadal lost his cool momentarily and argued furiously with the chair umpire when Berdych was awarded a point that Nadal felt should have been replayed.

“There is no argument,” Nadal said. “I am right, but it’s (a) mistake for him. But he is a great umpire and everybody (makes) a mistake.” The rare outburst only seemed to fire him up as Nadal dominated the tiebreaker and lost only one more game in the second set to take his round-robin record to 3-0.

“Doesn’t change nothing, that point,” said Nadal, who beat Berdych for the eighth straight time. “I think I still playing the same level before that point and after that point.” Roger Federer’s semifinal opponent will be decided later Friday when Andy Roddick plays Novak Djokovic. Roddick must win the match in two sets to stop Djokovic from claiming second place in Group A.

Nadal, meanwhile, remains on track to meet longtime rival Federer in what would be a dream final at the O2 Arena.

Having lost all three matches on the same court last year, Nadal seems to be getting to grips with the surface.

“Finish the season winning all the matches in the group, three victories against top-eight players in probably the most difficult surface for me, is unbelievable now,” Nadal said. “I’m very happy how I am playing, how I improved during the tournament.” Berdych had impressed in a straight-set victory over Roddick on Wednesday, and came out firing again against Nadal, perhaps eager to avenge a three-set loss in the Wimbledon final earlier this year.

The sixth-ranked Czech earned two break points in the second game, but Nadal’s serve got him out of trouble and the Spaniard did not face another break point in the match.

While Berdych’s first-serve percentage never got above 50, his forehand was a constant threat, and he deservedly took the set to a tiebreaker — but not before the match’s flashpoint moment.

Berdych’s backhand was called out by Brazilian umpire Carlos Bernardes, but Nadal had returned the ball in play.

Berdych challenged the call, which confirmed the ball was actually in. The Czech player was then awarded the point.

Berdych said later he thought Nadal had stopped playing to indicate the ball was out, and that the umpire was correct to give him the point.

“The referee is probably scared of him and just let him to talk with him too long,” Berdych said. “He was able to play. But every time when you just raise your hand, that means that you stop the play.” Nadal was convinced the point should have been replayed, and ranted first at Bernardes and then at the tournament supervisor sitting in the front row of the crowd, to no avail.

He reluctantly returned to the baseline to serve at 15-30 and when a fierce forehand drew an error from Berdych, Nadal pumped his fist and yelled his approval.

He was never troubled again. Serving for the win at 5-1, Nadal even had the confidence to try a through-the-legs winner, and although that dropped millimeters wide, he still finished with 27 winners to Berdych’s 18.

In doubles, Lukasz Kubot and Olivier Marach beat Daniel Nestor and Nenad Zimonjic for their first win in the group, but the Polish-Austrian pair were already eliminated while No. 2-ranked Nestor and Zimonjic were already through to the semifinals. Later, Mahesh Bhupathi and Max Mirnyi were to play Wesley Moodie and Dick Norman for second place in Group B.