World No. 1 Rafael Nadal stunned Andy Roddick with a stunning fight back to win 3-6 7-6 (7-5) 6-4, to claim his first victory ever at the O2 Arena in the ATP World Tour Finals.

During the debut of the championship last year in London, Nadal had lost all three matches in the group stages leading to doubts about his future in the game. However, he responded with one of the greatest season's a tennis player can dream of, winning 3 grand slam titles among others.

His barren run at the O2 Arena looked set to continue, however, as Roddick displayed composure, despite a majority of the 17,500 capacity crowd rooting for the World No. 1, to break Nadal in as early as game two. He followed that up with three consecutive aces in game three before taking the first set with a commanding 3-6.

Nadal displayed exactly why he is World No. 1 in the second set. Roddick broke him early in the set to go 2-1 up. However, the Spaniard took advantage of a stuttering Roddick, who double faulted in the following game, to get back to 2-2. The set went on to a tie-breaker, which Nadal claimed 7-5 to take the game to the final set.

The World No. 1 had found his rhythm by this time and he took the initiative and attacked the second ball. He broke at 3-2 to set himself on his way to his first win in his first game for five weeks.

In the earlier game, Novak Djokovic made an easy job of 6th seed Tomas Berdych cruising past the Croatian 6-3 6-3 to place himself for a qualification to the semis.

Berdych looked nervous competing in his first ever ATP World Tour Finals and it showed in his game after he double-faulted twice early in the first set to hand Djokovic the advantage. It was much the same in the second set and the Serb was rarely threatened as he won his opening tie.

When you have a first appearance at such a big tournament it's not easy to handle the pressure and expectations, and you could feel that, especially at the start of the match, said Djokovic.

He made two double-faults in the opening game and to start off with a break was really important for me. I was trying to focus on my game and do the things I planned to do tactically with my coach, and I couldn't ask for a better start to the tournament.

Djokovic also revealed that he is keeping his mind off his Davis Cup final next week. He said, Playing in a Davis Cup final is the biggest success that my country has ever had but I'm managing to control my emotions and my focus towards this tournament. I'll think of Davis Cup when I finish with this.

Berdych has had a mixed season which saw him playing some of his best tennis in the first half of the year, capped by an appearance in the final of Wimbledon, before drastically losing form in the second half.

He admitted to having butterflies in his tummy at the thought of competing in a major event as the ATP finals. He said, If I said 'no' I would be lying. I think you can see at the beginning it affected my game a little bit, but it was the first match and that's the way it is.

It's tough to come here after a couple of months when I didn't win too many matches and you're struggling with confidence. You can practice hard but the confidence you can't get anywhere else apart from winning matches.

To play Novak in the first match, it's really tough, but that's how it is and in the next two matches anything could happen. If you win the next match it gives you so much more confidence than winning the first match in a basic tournament.

Berdych next faces Nadal in the round-robin stage, while Roddick and Djokovic promise a thriller.