Former US Open champion Sloane Stephens overcame gallant Kiki Bertens in another marathon match at the WTA Finals, a result which breathes life into Japanese sensation Naomi Osaka's teetering Singapore campaign.
The American struggled mid-match but fought back from an early break in the third set to prevail 7-6 (7/4), 2-6, 6-3 in two hours and 20 minutes.
It was the result crowd favourite Osaka needed after she fell to number one seed Angelique Kerber in a three-set classic to put her on the brink of elimination.
Like White Group, all players from Red Group can still qualify for the semi-finals although winless Osaka will need to rely on results to get through.
World number six Stephens has moved into pole position after her second straight victory.
"I just tried my very best from the first point in the third set and it didn't go my way immediately but I just kept battling," she said after the match.
It was the sixth consecutive match to go the distance at the unpredictable WTA Finals.
Earlier, Kerber had a chance to serve it out against Osaka in the second set but triumphed the hard way in a pulsating 6-4, 5-7, 6-4 victory in two hours and 30 minutes.
The German appeared to be hampered by a back injury in the third set but dug deep and gained the crucial break in the seventh game.
"I will try to recover as soon as possible," Kerber told reporters. "It was just one, two points which decided the match. I'm just happy that I won the battle."
Osaka seemed to struggle at times with a left hamstring injury.
"It doesn't feel good... it's nothing that concerning, I think," she said. "This match was sort of a continuation of my last match in a way... that I didn't serve well."