Jack Sock stays in #ATPFinals hunt by beating Cilic

Roger Federer Alexander Zverev

Roger Federer Alexander Zverev

After Sock's win, Federer can claim his 14th year-end semi-final from 15 appearances at the season wrap-up if he beats Zverev, 16 years his junior, in straight sets.

Jack Sock kept his dreams of a fairytale finish to his season alive on Tuesday, beating Wimbledon finalist Marin Cilic 5-7 6-2 7-6 (4) at the ATP Finals.

Jack Sock recorded an enthralling three-set victory over Marin Cilic to enhance his chances of progressing past the round-robin stages of the ATP Finals.

Serve dominated the rest of the set but Cilic edged 4-2 up in the tie-break when the ball struck the net chord and Sock failed to dig it over.

"That was a tough one for sure", said Sock. "The fire alarm went off at 4am so it's been a long morning". It is what it is, you have to deal with it. Marin's an incredible player, he's had an fantastic season but I was able to get through. But I love playing here in London, it's an awesome atmosphere, you make me feel like home. I'm excited to get the win and stay alive.

He may still have to beat Zverev in his final group match to qualify, with the talented German going up against favourite Roger Federer later on Tuesday.

Sock, the American number one, came from nowhere to reach the end-of-season event, reaching London by winning the Paris Masters - and breaking a run of European success at Masters events stretching back to 2010.

Zverev is the only man to have won a match against Federer when ranked inside the top-10, while he's also the only star to topple the Swiss in a final, after downing him in Montreal.