Former world number one Roger Federer has admitted that he was "worried" about being defeated by Mardy Fish after the American forced through a third set.
The 30-year-old recorded a third consecutive win in the ATP World Tour Finals by overcoming the world number eight 6-1 3-6 6-3.
"I've played Mardy a few times and he's always very dangerous," said Federer. "He takes the ball extremely early, serves great and can get on roll. I was worried in the third set.
"I thought I was going to lose today but I'm very happy. It's been a great run since the US Open - I've been all round the world but I'm still going strong. Hopefully I can make it a nice weekend."
The winner of the Rafael Nadal and Jo-Wilfried Tsonga clash this evening will join the Paris Masters champion in the semi-finals in London.
