Federer fights past Zverev

Roger Federer held young pretender Alexander Zverev at bay in a gripping contest Tuesday to reach the last four of the ATP Finals and stay on course for a seventh end-of-season crown.

The world number two saw off a spirited challenge from the much-hyped German 7-6 (8/6), 5-7, 6-1 in front of a boisterous pro-Federer crowd to become the first man through to the last four at the O2 Arena.

"It was a good battle and I always enjoy myself at this beautiful arena," said Federer, who has now reached the semifinals 14 times.

"I have so much fun playing in London and I have been so successful here. Thank you for making it such a special night.

"I'm happy and relieved that I can play freely against (Marin) Cilic, instead of it being a nailbiter. It's been a tough group so to be through in two matches is great."