London - World number one Novak Djokovic recovered from a slow start to defeat Tomas Berdych 3-6, 6-3, 7-6 (7/3) in his opening match at the ATP Tour Finals on Monday.
Djokovic, who joins David Ferrer at the top of Group A, has enjoyed a remarkably successful season but he had to show all his battling qualities to subdue the big-hitting Czech in over two and a half hours on court at London's O2 Arena.
The 24-year-old Serb has enjoyed one of the greatest single seasons in tennis history after winning three Grand Slam titles and five Masters crowns during a remarkable run of 69 wins from 73 matches.
His incredible consistency has deservedly lifted him to the top of the world rankings and a second triumph at the ATP's season finale would be a fitting way to end such a majestic campaign.
He will need to improve on this inconsistent effort but his spirit is still strong judging by the gutsy way he fought back from a set down.
Djokovic, who won the Tour Finals in Shanghai in 2008, has been struggling with back and shoulder injuries since winning the US Open and was forced to withdraw from the recent Paris Masters as a result, yet he never looked like waving the white flag in the face of Berdych's early assault.
Berydch, whose only win in eight meetings with Djokovic came in the 2010 Wimbledon semi-finals, took the attack to Djokovic in the first set and the aggressive gameplan paid off as he broke to open up a 2-0 lead.
Djokovic had no answer to Berdych's ferocious ground-strokes in the fourth game either and he conceded another break when a tame backhand from the Serb limped into the net.
But Djokovic has shown he has the character to grind out wins during his glorious run this year and he capitalised on a sloppy service game from Berdych to get one of the breaks back immediately.
That seemed to lift Djokovic out of his early slumber and he troubled Berdych again in the seventh game. This time however the Czech's big serve got him out of trouble as he saved three break points.
Berdych's serve is a formidable weapon when he is on song and those booming deliveries were enough to keep Djokovic at bay and close out the first set.
Even so there was a growing sense that Djokovic was starting to hit his stride and he underlined that impression with an early break in the second set.
Djokovic was serving with far more accuracy now and there wasn't even a glimmer of hope for Berdych as the Serb easily held onto that advantage to force a decider.
A tense final set seemed to have shifted Berdych's way when he broke for a 4-2 lead, but Djokovic hit straight back with a break of his own.
Berdych couldn't convert a match point when Djokovic served to take the match into a tie-breaker, which the Serb took with his customary combination of belligerence and brilliance.