World No. 1 Rafael Nadal came from one set down to beat American eighth seed Andy Roddick 3-6, 7-6(5), 6-4 in his opening match at the ATP World Tour Finals on Monday.

It's also the Spaniard's first win at the O2 Arena in London, as he lost three matches in the round-robin group here last year, even without taking one set.

Nadal admitted that last year's straight defeats were still in his mind and he felt nervous at the beginning of Monday's match.

“When you start a tournament like this one that you play against the best players of the world, I said before, in the more difficult conditions for me, is the last part of the season that I normally never played my best tennis," said Nadal.

Nadal was shaking while Roddick was rocking.

The American took four points in a row to win the opening game after Nadal grabbed two break points, then claimed victory in the world No.1's first service game mainly due to the two double faults of Nadal.

But Nadal seemed finding his rhythm as the match went on. Although he was broken earlier in the second set, he managed to send one back immediately before played toughly to win the tiebreak.

"It's a very positive victory for me and very, very important," said Nadal who have never won the season finale, even though he had completed his Grand Slam titles and also got an Olympic gold medal.

Earlier, the world No. 3 Novak Djokovic of Serbia defeated the season finale debutant Berdych in style as he only required 88 minutes to wrap it up 6-3, 6-3.

"I couldn't ask for a better start of the tournament," said the 23-year-old Djokovic, winning the event in 2008.

Berdych 25, is the only player in the Top 10 not to win an ATP World Tour title this season. Although he defeated Djokovic in straight sets in the Wimbledon semifinals this year, he lost to the Serbian in Davis Cup semifinals later.

Berdych admitted that he felt pressure as it was his first ever match in the season finale. "If I would say no, then I would be lying. So, yes, I think you can see in the beginning that there was a little bit of, like, it affect my game a little bit," said the world No. 6 who made two double faults in the opening game and was broken easily.

Then, Berdych fought hard in the third game of the first set and finally took the game after saving four breaking points, but couldn't stop Djokovic breaking again in the ninth game.

As the semifinalist at French Open and runnerup at Wimbledon, Berdych played better in the second set but still lost it for being broken in the second game.

"If you just give him more pressure, then, you know, he could make