Jo-Wilfried Tsonga earned his first win at the ATP World Tour Finals on Tuesday, beating Mardy Fish of the United States 7-6 (4), 6-1 in his second Group B match.
Fish seemed to be slowed down by the left hamstring injury that has disrupted the end of his season, while Tsonga struggled to find consistency.
The sixth-seeded Frenchman was twice up a break in the first set before finally taking it in a tiebreaker. Tsonga was broken at love to start the second set but then reeled off six straight games.
Defending champion Roger Federer was to face longtime rival Rafael Nadal later Tuesday at the O2 Arena.
Tsonga's win means that Federer will qualify for the semifinals if he comes out on top. Nadal will be guaranteed progress only if he wins in straight sets.
Fish followed his opening three-set loss to Nadal with a second straight defeat.
The 29-year-old American hit his troublesome left leg with his racket several times during Tuesday's match, although the pain didn't stop him attempting a through-the-legs shot in the tiebreaker and running full pelt across the court to reach a short ball toward the end of the second set before athletically vaulting the courtside bench.
Tsonga, beaten in three sets by Federer in his opening match, had a chance to serve out the first set at 5-4, but sent an ambitious drive volley into the crowd from the frame of his racket on his way to being broken for the second time.
That was one of 21 unforced errors for Tsonga, but his 33 winners, including a glorious backhand pass to take a decisive 3-1 lead in the second set, were enough to beat a fading Fish.