London - Jo-Wilfried Tsonga remains in the hunt for a place in the semi-finals of the ATP World Tour Finals after the French sixth seed defeated America's Mardy Fish 7-6 (7/4), 6-1 on Tuesday.
Tsonga, who lost his opening Group B match against Roger Federer, still has to beat Rafael Nadal in his final fixture on Thursday to have a chance of advancing, while Fish faces an early exit from the season finale at London's O2 Arena.
The result also means defending champion Federer will be guaranteed a semi-final spot if he defeats Nadal in tonight's match.
With both players beaten in their opening games, this encounter was a battle for tournament survival as the loser would be eliminated.
Tsonga started in aggressive mood, earning three break points before finally breaking at the fourth attempt with a brilliant winner on the run.
The 26-year-old had outlasted Fish to claim a five-set victory in their only previous meeting, in the US Open fourth round earlier this year, and this was another rollercoaster clash.
Fish broke straight back in the next game, only for the American eighth seed to surrender his own serve again to give Tsonga a 2-1 lead.
Tsonga became the first player to hold serve in the next game, but the often-erratic Frenchman crumbled when he served for the set.
Fish had an animated discussion with the umpire between games and letting off some steam seemed to do him good.
He knocked Tsonga out of his stride with a magnificent top spin lob and levelled the score on his second break point when the sixth seed sent a backhand long.
It needed a tie-break to decide the set and Tsonga took it with a pair of big serves to take advantage of his mini-break.
Fish, playing in the Tour Finals for the first time, has been struggling with a hamstring problem recently and he appeared to be running out of steam in the second set.
The American started with a break in the first game, but couldn't maintain his momentum and allowed Tsonga to break straight back.
Both players were mixing in far too many unforced errors between their occasional moments of brilliance, but Tsonga produced enough pressure with his groundstrokes to convert on his third break point for a 3-1 lead.
That blow shattered Fish's morale completely and Tsonga broke again before serving out the match.