LONDON, Nov. 14 (Xinhua) -- Marin Cilic defeated American John Isner in three sets 6-7(2), 6-3, 6-4 to keep alive his chances of qualifying for the semifinals of the ATP Finals in London.

The Croatian dealt well with Isner's powerful serve and errors towards his victory in two hours and 14 minutes.

The decisive spell in the match came when Cilic scored three consecutive breaks against Isner at the end of the second and the beginning of the third set and was able to serve out to claim the win.

The fact Cilic won in three sets means that world No. 1, Novak Djokovic becomes the first player to book his place in the semifinals after he continued his winning streak with a 6-4, 6-1 win over Alexander Zverev in an hour and 16 minutes earlier in the day.

Djokovic, who is attempting to win the trophy for a record equalling sixth time, may have only hit one ace in comparison to Zverev's nine, but still won a decisive 75 percent of his first serves.

"I thought I played well from mid-way through the second set. I started to swing through the ball. I haven't served that great. He obviously made a lot of unforced errors that allowed me to win easier than expected," said Djokovic. Enditem