Kiki Bertens believes she is capable of beating anybody after reaching the last four of the WTA Finals.

Bertens is only playing in Singapore due to Simona Halep's late withdrawal, but the Dutch debutant has grabbed the opportunity with both hands.

The world number nine moved into the semi-finals when Naomi Osaka retired from their final Red Group match due to a hamstring injury, after the US Open champion had lost the first set on Friday.

Bertens now has 12 victories against top-10 players in an impressive season, so the 26-year-old will have no fear when she faces Elina Svitolina or Karolina Pliskova with a place in the final at stake.

"I think it's just proof to myself that I can beat anyone. I think that's a really nice feeling," Bertens said.

"I think before I really had [the feeling] like, 'Oh, those are great players, and I can never beat them.' Now, I'm still thinking those are great players but I have beaten them before, so I can do it, so hopefully I can do it again. I think it helped me a lot with the confidence."

Looking ahead to her semi-final tie, she added: "Both matches would be really tough. I played Karolina a little bit more this year than Svitolina. They played really well here, I would say. So I have to play a high level again and just give it all."

Bertens expressed her sympathy for Osaka, but welcomed the opportunity to get some extra rest ahead of her semifinal.

"When she called out the physio, I think the last point [before that] she was not moving to the ball like from 4-3 to 5-3. But before that, I didn't know [she was injured]," Bertens added.

"I saw her in the match before, that she was struggling a little bit with the hamstring, and of course she was taped today, but I think in the beginning she was still okay."

"It's never easy or never nice to win a match like this, but it is what it is. I'll take it and I'll take my rest, and I have some more recovery time."