Tomas Berdych reignited his ATP World Tour Finals challenge with victory over out-of-sorts US Open champion Marin Cilic in London.
Czech Berdych won their crucial Group A contest 6-3 6-1, after both men lost their opening matches on Monday.
Novak Djokovic and Stan Wawrinka meet in Wednesday's late match, with a first semi-final place up for grabs.
Berdych will play Djokovic and Croat Cilic faces Wawrinka in Friday's final round-robin matches.
Two heavy defeats mean Cilic is all but out of the tournament, leaving Berdych to try and take one of the semi-final places from Wawrinka or Djokovic.
"I was really trying to focus on my tennis and my game, trying to go point by point," said Berdych.
"Today was more fighting and getting through. It's good to have a win and it always counts.
"It's not my first year. I have the experience of losing the first match in the past and I know how to come back. That was the biggest difference today."
The crowd was noticeably down on previous matches as the two group outsiders returned to the scene of Monday's humiliation, when between them Berdych and Cilic won just four games and managed one hour and 54 minutes of action.
If nothing else, they at least managed to stay on court for one hour and 14 minutes second time around.
Berdych also extended his remarkable record of having lost all five of his opening matches at ATP Finals, yet won all five of his second matches.
The pair continued in the same vein as Monday in an error-strewn opening game that lasted seven minutes and ended with Cilic netting a forehand when facing a fourth break point.