Roger Federer "really happy" with opening win at ATP World Tour Finals

Roger Federer has admitted that he was delighted to get off to a winning start at the ATP World Tour Finals in London.

On Sunday, the second seed ran out a 6-4 7-6 winner over Jack Sock - who is making his debut at the event - to take the first step towards claiming a seventh title.

Federer was competing for the first time in two weeks after choosing to withdraw from the Paris Masters, but the Swiss was happy to come through without dropping a set against the big-serving American.

The 36-year-old is quoted by BBC Sport as saying: "I got off to a great start, my big hope was I was going to be able to play a bit more freely after that.

"The second set was tight, I missed some opportunities, the breaker could have gone either way and in the end he helped me with some double faults and some mistakes. I'm really happy that I got through somehow."

Federer will now face Alexander Zverev in his next group game after the young German came through in three sets against Marin Cilic.