Bengaluru, November 15: America's Jack Sock kept his ATP World Tour semifinals hopes alive with a 5-7, 6-2, 7-6 (7-4) win against big-serving Croatian Marin Cilic.
Cilic, who won the 2014 US Open and reached the Wimbledon final this year broke Sock twice to win the first set but found himself adrift in the second set as the 25-year-old levelled the round-robin match with two breaks of his own.
In a see-saw deciding set, the Croatian fifth seed was quickly out of his blocks, racing to a 3-0 lead before Sock, the eighth seed, steadied himself, cancelling out the break.
The match then settled back on serve and went into a tie-break and Sock emerged as the winner.
The American No.1 came from nowhere to reach the end-of-season elite eight-man field, by winning the Paris Masters -- and breaking a run of European success at Masters events stretching back to 2010.
Sock lost his first match in the Boris Becker group to Roger Federer while Alexander Zverev defeated Cilic, leaving both fighting for their lives .
After the win, Sock sounded upbeat about his last-four chances at the London 02 Arena," "I think if I do the right things and play the right tennis, I can give myself a chance to play on the weekend of any tournament. I think I've showed that more this year," said Sock, who won three ATP World Tour titles this season.