SINGAPORE: Karolina Pliskova was delighted to secure a WTA Finals last-four berth with one White Group match to spare after Tuesday's 6-2 6-2 victory over Garbine Muguruza enabled the Czech a chance to relax ahead of her last round-robin tie.

"I'm just happy that I don't have to play the next match for qualifying, because last year I was playing for it and it was pretty stressful," the world number three told reporters as she remembered her agonising defeat to Agnieszka Radwanska in 2016.

"So always happy, you know, that if I can win few matches in a row, it give me always extra confidence. Even today was not the best, but still I won so it counts," she added after following up her opening day victory over Venus Williams.

"There is one more match to go in the group, which I want to try to enjoy, not to lose, but just to try to enjoy the tennis a little bit more."

Pliskova, who still has a chance to end the season as the world number one, admitted it was difficult for her and Muguruza to go on court after Williams and Jelena Ostapenko had battled out a three-setter that lasted more than three hours.

"I'm just happy that we didn't play for the next three hours, because we were waiting for quite long. So always good to finish as soon as possible," the 25-year-old added.

"It was pretty tough, because we were waiting so long. There was already match point in the second set and then it went so long that we were both a little shaky in the beginning of the match, a little bit nervous and maybe a little bit tired.

"Next time, I probably won't watch that much tennis before my match. It's always tough to go after a match like this and especially that late. Some people had left so the atmosphere was not as good as if we had played first."

Muguruza beat Ostapenko in her opening match but was completely flat against Pliskova and the Spaniard is hoping to regroup before her all-or-nothing showdown against the 37-year-old Williams for a semi-final berth on Thursday.

"I'm not going to think a lot about this match, because it's one of those days when your opponent is playing good and your tennis is not at the level it should be to play against this type of player," the world number two said.

"I'm just going to concentrate on my next match, because I know I still have a chance. I'm not a big fan of this round-robin format but now it can help me turn things around, so that's honestly what I'm thinking right away."