LONDON, Nov. 16 (Xinhua) -- German Alexander Zverev booked a place in the semifinals of the ATP Finals in London after a 7-6(5) - 6-3 win over American John Isner in an hour and 17 minutes on Friday.

Zverev will play Roger Federer in the last four and leaves Marin Cilic with no chance of making it out of the Guga Kuerton Group, even though Cilic still has to play Novak Djokovic on Friday night.

Djokovic meanwhile is already assured of a semifinal tie against Kevin Anderson on Saturday evening.

Zverev was able to hold his serve throughout his match against Isner and won the match after taking the only chance he had in the second set to break the American's serve in a meeting between two big hitters.

Serve dominated the opening games with five completed in just 14 minutes and the two players rattling through their service games to take the set to a tiebreak, which was decided when Isner hit a mid-court forehand into the net.

The American had needed a straight set win to have any chance of making the semifinals and that error ended his options of reaching the last four.

"I am unbelievably happy to be through to the semifinals. John (Isner) is such a tough opponent. The last two matches for him against Cilic and me could have gone either way. The first set was unbelievably tight. I am just happy to be through. I will prepare myself the best for tomorrow," said Zverev after the game.

"I really wanted to come out and be aggressive. Play the best game I can and give myself the best chance to be in the semifinals. That's what I did and I am very happy about that," he added.