Singapore - A tenacious Angelique Kerber overcame a second set stutter to outlast Naomi Osaka on Wednesday, leaving the Japanese sensation's WTA Finals campaign hanging by a thread.
Kerber had a chance to serve it out in the second set but triumphed the hard way in a pulsating 6-4, 5-7, 6-4 victory in 2 hours and 30 minutes at the Singapore Indoor Stadium.
The Wimbledon champion appeared to be hampered by a back injury in the third set but dug deep and gained the crucial break in the seventh game.
After losing to Sloane Stephens on Monday, crowd favourite Osaka will need to rely on results in Red Group to have a chance of qualifying for the semi-finals.
Kerber bounced back impressively after a shock defeat to Kiki Bertens.
"I think we both played at a high level tonight," Kerber said after the match.
"I had my chances in the second set but she played unbelievable. In the third set it was just one or two points that decided the match."
With plenty at stake, both players made a nervous start in an error-riddled opening culminating in three straight breaks of serve.
An aggressive Osaka went for her shots but couldn't find her irresistible range and a patient Kerber made her pay.
Much like against Stephens, a frustrated Osaka threw her racquet in disgust midway through the first set.
The experienced Kerber had all the answers, utilising her forehand down the line to great effect.
A rejuvenated Osaka made her move in the second set breaking Kerber twice but she was unable to consolidate on serve.
Kerber capitalised and unleashed a barrage of winners against a flat-footed Osaka, who appeared bothered by her left leg.
Kerber served for the match at 5-4 but Osaka blasted a flurry of winners to break back.
She once again broke a flustered Kerber to take it into a third set for the first time between the pair.
Osaka had the momentum early in the third set but played a loose seventh game to drop serve and hand Kerber the defining break.
It was Kerber's fourth straight victory in the match-up between the past two Grand Slam winners.