- Novak Djokovic beats Tomas Berdych in a third-set tie-break in Group A opener
- Serbian saves a match point to triumph at the season-ending championships
- Fifth seed David Ferrer upsets home hope Andy Murray in Monday's first game
- World No. 3 Murray struggling with groin injury and may quit the tournament
World No. 1 Novak Djokovic saved a match point before finally overcoming Tomas Berdych in his opening match of the ATP World Tour Finals in London on Monday.
The Serbian triumphed 3-6 6-3 7-6 (7-3) against the seventh-ranked Czech in two hours and 40 minutes, after an injured Andy Murray went down to 2007 runner-up David Ferrer in the day's first Group A fixture.
"Throughout most of the match he was the better player, I was just hanging in there and I managed to get the win," Djokovic said.
"You have to be top of your game in order to win the matches in this event. I wasn't on top of my game but I managed to take my chances."
Berdych beat Djokovic in the 2010 Wimbledon semifinals but had lost their seven other encounters on hard courts.
He raced to a 4-0 lead in the first set as his opponent looked rusty after pulling out in the Paris Masters quarterfinals due to shoulder problems which have worried him since winning the U.S. Open in September.
Djokovic came back strongly in the second, and had to battle back from 4-2 down in the decider and then escaped at 6-5 on his own serve as Berdych hit the net with a forehand.
The 26-year-old made more nervous errors in the tiebreak as Djokovic went 5-1 clear, inexplicably hitting another forehand wide and then smashing a volley long.
It was Djokovic's 70th win in 74 matches this season, in which he has won three of the four grand slam events and toppled Rafael Nadal from the top of the rankings. He won the season-ending championships in 2008 before it moved from Shanghai to the UK capital.
The 24-year-old is second in the group after Ferrer's straight-sets win, but can redress that when he meets the Spaniard on Wednesday.
World No. 3 Murray said he will decide on Tuesday whether he will be fit enough to continue against Berdych after struggling with a groin injury during his 6-4 7-5 defeat by Ferrer.
"You've got to sometimes do the right thing. I didn't know exactly how it was going to feel on the court today," the Scot said after his second defeat in 19 matches since the U.S. Open -- the other one came against Berdych in Paris this month.
"I haven't been able to do too much training this week. I played, I didn't feel particularly great. I'll see if I feel any better tomorrow."
Fifth-ranked Ferrer was delighted after ending a run of four defeats to Murray.
"I'm very happy. I beat Andy, in London, in his home. It is not easy. I played very consistent all the match," he said.
"I think it was important to start winning the match, and if you win in two sets it is better with the group. You know you need to win one more match, because it is very difficult to reach the semifinals winning only one match. I think this tournament is very, very special. It is very important."
Top doubles seeds Mike and Bob Bryan won their opening Group A match, with the Americans beating seventh-ranked U.S. Open champions Jurgen Melzer of Austria and Philipp Petzschner of Germany 6-7 (4-7) 7-5 10-7.
Indian fourth seeds Mahesh Bhupathi and Leander Paes suffered a surprise 7-6 (8-6) 6-1 defeat by the sixth-ranked debutant pairing of Sweden's Robert Lindstedt and Romania's Horia Tecau.