Jack Sock kept his hopes alive in the ATP finals with a courageous display, emerging from the brink of defeat to beat Marin Cilic 5-7 6-2 7-6(4) in a dramatic if erratic battle of the big hitters at London's O2 Arena on Tuesday.
With these two powerful customers desperate to keep their hopes alive after losing their opening matches, it was the American, in his debut finals, who held his nerve best in the decisive tiebreak after a compelling 2 hours 27 minutes contest.
Cilic, who had also blown a fine chance of an opening day win over Alexander Zverev on Sunday when leading 3-1 in the deciding set, again capitulated when 3-0 up in the decider.
Sock, who had been beaten in straight sets by Roger Federer on Sunday, came from a set down and, despite being on the wrong end of a couple of unfortunate net cords, kept his cool even when going 4-2 down in the tiebreak.
Ultimately, the more experienced Croat Cilic, who has a poor record in the end-of-season finals, proved just too erratic, mixing his 35 outright winners with 37 unforced errors.
Federer will be meeting Zverev later on Tuesday in the other match in the Boris Becker group.
Sock keeps hopes alive with win over erratic Cilic