Kiki Bertens stunned reigning Wimbledon champion Angelique Kerber to claim a thrilling victory on day two of the WTA Finals in Singapore.

The 26-year-old Dutch player triumphed in three sets, recovering superbly from dropping the opener 6-1 by winning the next two 6-3 6-4.

It was Bertens’ singles debut in the WTA Finals, and her Red Group victory came in just over two hours.

“I am really happy to get the win,” world number nine Bertens told

“It was a slow start, but I was really happy to turn around this match.

Angelique KerberAngelique Kerber suffered a defeat to Kiki Bertens in Singapore (Jonathan Brady/PA)

“I had a little chat with my coach when it wasn’t going so well, so we decided to go a little bit more for my shots, play a little more aggressive and it worked out.”

Earlier, Sloane Stephens won the battle of the last two US Open champions to beat Naomi Osaka 7-5 4-6 6-1.

American Stephens, the 2017 US Open champion, edged a fiercely competitive 51-minute first set which produced no less than five breaks of serve.

Osaka levelled the Red Group match after enjoying two early breaks in the second set.

But the 2018 US Open champion from Japan was eventually overpowered as Stephens secured victory in two hours and 24 minutes.

“I knew from the very beginning it was obviously going to be a tough match, so I was going to have to stay in a lot of long points and make sure that I made a lot of plays on the ball, which I did,” Stephens said.

“I thought when she was hitting good shots, I got my racket on a lot of the balls and I just made her play an extra ball.

“We played a lot of great long rallies, and she played a lot of great short points.”