Agnieszka Radwanska has never lost a match against Karolina Pliskova, but does not believe that will count for much when they vie for a place in the last four of the WTA Finals in Singapore on Friday.

After slipping to defeat in her opener to Svetlana Kuznetsova, defending champion Radwanska beat Garbine Muguruza in straight sets on Wednesday.

The result sent Muguruza out of the competition and means the winner of the Pole's meeting with Pliskova on Friday will join Kuznetsova in advancing to the semi-finals from the White Group.

Radwanska has won all six of her previous meetings with the Czech without dropping a set, but she expects it to be tight this time around.

"I think it's going to be a good challenge for me on Friday, playing someone like her [Pliskova]," said the world number three.

"She had a great season, playing very solid tennis. We will see how it's going to be.

"Those last matches were really, really tight. I remember the match from Stuttgart [a 6-2 7-6 (10-8) win for Radwanska this year] – that was a good one with a crazy tie-break as well. It's always very tight."

Muguruza was disappointed to have bowed out of the competition after just two matches but credited Radwanska for making it tough.

"I think I could have played a bit better in important moments, but she was playing amazing shots so it was difficult for me. I think this court suits her very well, it's just a tough opponent," said the Spaniard.

"The way she plays. She makes you think, she makes you vary a lot.

"My warm-up was not pretty good, I just didn't feel like other days. But in the match I felt good.

"I think she's very solid. She doesn't miss a lot. She's everywhere in the court. She has a good eye so she can read where you're going to play and she goes before you going to hit, and then she comes with a lot of incredible shots and she has a lot of talent."