Federer chases ton but Djokovic on form
Germany's Alexander Zverev clinched the last spot in the ATP Finals semi-finals by beating John Isner and ensured world number one Novak Djokovic finished as group winner.
Zverev nicked a first-set tie-break before breaking at the end of the second to win 7-6 (7-5) 6-3 in London. Third seed Zverev will play Roger Federer in the semi-finals today.
Djokovic, who beat Marin Cilic 7-6 (9-7) 6-2 later yesterday, will play South Africa's Kevin Anderson.
The 14-time Grand Slam champion is the heavy favourite to win the tournament after easing through the round-robin stage with three victories.
Federer insists the prospect of claiming his 100th title in London is still not entering his head.
The Swiss great needs one more title to make it a century of career singles tournament wins, but with Zverev finishing the year strongly and Djokovic in irresistible form, he knows it will be a tough ask at the O2 Arena.
"Personally I'm still not thinking of the number 100," said the 37-year-old, six times a winner at the ATP Finals.
"I won't let that get in my head, make me go crazy, because it should be something I'm excited about and not something I should feel extra pressure.
"As long as I think Novak is in the draw anyhow, he's playing so good again, it's never going to be easy."
In the doubles, Pierre-Hugues Herbert and Nicolas Mahut won their group by beating Mike Bryan and Jack Sock 6-2 6-2 in 53 minutes. Bryan and Sock finished second and will face Britain's Jamie Murray and Bruno Soares in the semi-finals.