Novak Djokovic has won his opening match at the ATP Tour World finals but needed a tiebreak to defeat Tomas Berdych.
The world number one survived a match point on his serve to defeat the Czech 3-6 6-3 7-6(3).
Berdych produced some fabulous hitting to take the first four games of the opening set and despite the Serbian breaking back, he claimed the set 6-3.
The four-time Grand Slam winner then took the second set by the reverse scoreline, breaking Berdych early on and then holding serve conmofortably to level proceedings at 1-1.
Berdych broke the Serbian's serve again midway through the final set but Djokovic fought back to take it to a tiebreak.
Having played so well throughout, the Czech then made a string of errors as Djokovic took the tiebreak 7-3 to claim victory at the O2 Arena.
