World number one Novak Djokovic clawed his way to victory over Tomas Berdych in his opening match at the ATP World Tour Finals on Monday but Andy Murray's prospects look bleak after a groin injury flared up in his shock defeat by David Ferrer.

While the atmosphere in the O2 was a little flat as Murray laboured, it was electrifying in the night session as 17,500 fans, many waving Serbian and Czech flags, crammed into the huge arena that will stage the event until 2013.

Despite having blue tape plastered over his shoulder, Djokovic said he had suffered no recurrence of the injury that forced him to withdraw from the Paris Masters this month.

"Something I'm happy about is my condition," he said. "I haven't felt any pain in my shoulder. I'm exhausted because it was three hours but I feel physically fit."

After levelling the match with consecutive aces at the end of the second set, Djokovic found himself in trouble again in the third against the raw power of Berdych.

However, the Czech's tendency to crack at key moments returned to haunt him. He let Djokovic off after forging a 4-2 lead and then when a Djokovic double fault presented him with a match point at 5-6 he buried a forehand into the net.

Another slew of Berdych forehand errors in the tiebreak, one of them worthy of a park hacker, gave Djokovic breathing space and he sealed victory after two hours 38 minutes.

"Maybe I was too risky (on match point), but that's how I play," Berdych, who is due to face Murray next on Wednesday, told reporters. "That was my chance to end the match."

It would have been scant consolation for Berdych but the quality on display in the evening was far superior to that served up by Murray and Ferrer.

Murray briefly appeared to have got back on track when he broke to lead 2-0 in the second set and again to move 4-3 ahead but it proved a false dawn as the mistakes returned.

At 5-6, Ferrer reached match point with a nervy forehand volley which clipped the line and he converted at the first attempt, punishing his opponent for an ill-advised drop shot.

"I think it was important to start with a win," Ferrer told reporters. "I think he had some little problems, but not too many strong problems because he played the whole match."

Nadal and Roger Federer, both of whom won their opening Group B matches on Sunday, face each other for the 26th time in a mouthwatering evening session on Tuesday.