Defending champion Novak Djokovic recovered from a shaky start to beat Dominic Thiem in the first match of the ATP World Tour Finals on Sunday.
The 12-time grand slam champion is aiming to return to the top of the world rankings in London after his 122-week reign was ended by Andy Murray at the Paris Masters and battled back to defeat Thiem 6-7 (10-12) 6-0 6-2.
Thiem had never taken a set off the Serbian in their previous meetings, but came out on top in a marathon tie-break to take the opener before the second seed hit back in emphatic fashion in Group Ivan Lendl.
Djokovic, winner of the season-ending tournament in each of the last four years and five times in all, needed treatment for a cut thumb in the first set and was warned for unsportsmanlike conduct after Thiem deservedly won a tense breaker.
Umpire Carlos Bernardes issued the warning to the Australian and French Open champion when he hit a ball towards his player's box after going a set down.
That was as good as it got for eighth seed Thiem, as Djokovic harnessed his frustration by sweeping the tournament debutant aside in clinical fashion with a second-set bagel and two breaks in the decider to seal victory in just over two hours.
Djokovic  bt Thiem  6-7 (10-12) 6-0 6-2
Djokovic - 34/27
Thiem - 40/33
Djokovic - 3
Thiem - 4
BREAK POINTS WON
Djokovic - 5/6
Thiem - 0/1
FIRST SERVE PERCENTAGE
Djokovic - 68
Thiem - 67
PERCENTAGE OF POINTS WON ON FIRST/SECOND SERVE
Djokovic - 72/77
Thiem - 67/34
Djokovic - 101
Thiem - 75