Perfect Djokovic makes semis
Novak Djokovic powered into the semi-finals of the ATP World Tour Finals with a perfect record after beating Tomas Berdych for a third win out of his three round robin matches.
The world number one was in impressive form as he saw off Tomas Berdych 6-2 7-6 (8-6), after saving three set points in the second set.
Djokovic is now guaranteed to top Group A while Berdych is out, with Andy Murray securing his last-four spot on Friday night by with a straight-set victory over Jo-Wilfried Tsonga.
Berdych had beaten Djokovic only once in 11 previous meetings, in the semi-finals of Wimbledon in 2010, and he was soon under pressure.
Djokovic's famed returns were rushing the Czech and, although he clawed his way back from 0-40 in the third game, a fourth chance arrived and the world number one took it.
Djokovic, whose best performance at the O2 was a semi-final appearance in 2010, looked extremely sharp and he made it five games in a row before Berdych finally stopped the rot.
The top seed comfortably held to win the set, though, and with that assured himself qualification for the last four.
Berdych appeared to have no answer when Djokovic broke again in the third game of the second set but he began to take the fight to his opponent a bit more and hit back to level at 2-2.
Berdych made a flying start to the tie-break, winning five of the first six points, but Djokovic did not give up and saved two set points on his own serve before another trademark return at Berdych's feet levelled matters at 6-6.
The top seed then added a fourth point in a row and clinched victory when Berdych fired a return long.
With Djokovic's father continuing to battle a blood disorder, the Seb said: "It was hard to focus on tennis. It still is, but there is good news every day.
"That makes me happier, makes me play more relaxed on the court. I switch off on the tennis court. I try to think only about the match and it's been working well so far.
"Every win means a lot for my family and me. But there are more important things in life, and that's health. I guess that's the priority now."