Sloane Stephens downs Osaka in Singapore

SINGAPORE: A confident Sloane Stephens stormed to victory on Monday night with a commanding third set performance against Japanese sensation Naomi Osaka to highlight another night of stunning upsets at the WTA Finals in Singapore.

In an unpredictable encounter, the American overcame a second set stutter to dominate the decider and triumph 7-5, 4-6, 6-1 in two hours and 25 minutes.

It was followed by another marathon match with number eight seed Kiki Bertens overcoming top- seed Angelique Kerber in a thrilling 1- 6, 6- 3, 6- 4 comeback victory.

The lower seeds have won all four matches to start the WTA Finals.

Before Monday, Osaka had won 14 of her previous 16 matches to be the in-form player coming into the season-finale.

But the third seed was wildly inconsistent in the Red Group opener with 46 unforced errors and was broken three times in a third set meltdown.

Stephens handled the warm conditions better to record an impressive victory.

“It’s really humid inside the stadium, so it plays a little bit different,” she told reporters.

“Obviously playing someone with a lot of confidence is always a tough task, but I think that I played well and I kept a good attitude.”

Osaka lamented her errorstrewn performance.

“I think I made more unforced errors than her in the third set,” she said.

“I don’t really think you can do that against her, so definitely I think that’s what made the difference.”

It was a much-anticipated showdown between the past two US Open champions, who were making their WTA Finals debuts.