Djoko downs Berdych
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.
Novak Djokovic celebrates a point. PIC/AFP
Meanwhile, France's Jo-Wilfried Tsonga -- who lost his opening Group B match against Roger Federer � defeated America's Mardy Fish 7-6 (7/4), 6-1.
Murray may pull out
Andy Murray may have to pull out of the tournament after suffering a groin strain in practice last week and needed treatment on the problem during Monday's defeat to David Ferrer. He will decide in the next 24 hours whether he is able to continue.