SHENZHEN, China - No.2 seed Karolina Pliskova notched up her first Shiseido WTA Finals Shenzhen win in unfortunate circumstances as No.4 seed Bianca Andreescu was forced to retire after losing the first set 6-3.

The Canadian had just got off to a lightning start, overpowering Pliskova to break from 40-0 up in the first game and going up 2-0, 15-15, when she pulled up short after stretching to return a wide serve from the Czech. Though Andreescu would resume play after getting her left knee heavily strapped, her movement thereafter was visibly hampered.

"I didn't know it was really that bad," said Pliskova afterwards. "Of course, I feel sorry for her... I just felt I'm really in the match. I was ready to fight today, not to give it to her easy. Doesn't matter how bad injured she is, how bad she feels, I just wanted to win, get this victory to keep myself in the tournament, which happened, of course not in the best way."

Having won 11 out of a stretch of 14 points when injury struck, Andreescu would win just one of the next six games after returning to the court. The US Open champion fought valiantly, and her shotmaking talent is such that when her movement wasn't tested she was still able to blitz winners out of nowhere - but during an on-court coaching session after the fifth game, a tearful Andreescu told coach Sylvain Bruneau that although she wanted to continue, she had "heard a crack" and was unable to bend her knee at all.

Pliskova would continue to struggle with a few ill-timed double faults, but in the main was able to move the ball around the court sufficiently to test her hobbled opponent's movement, breaking twice before serving out the set with her third ace - at which point Andreescu would finally call it quits.

With one round-robin match still to play on Friday, the 19-year-old will still be able to continue in the tournament if she is able - although she cannot now progress out of the Purple Group. In terms of Pliskova's advancement scenarios, the result counts as a win - meaning that both she and Simona Halep will be at 1-1 going into their final round-robin match against each other, and will play off for the second semifinal spot behind Elina Svitolina.

"I think that's going to be a great matchup," said Pliskov of her next challenge. "Should be incredible match. I hope it's going to be a good match to watch, too. I'm sure, because she's putting a lot of balls back. The tennis with her, I feel it's always good to watch. Of course, for me tough because there's going to be a lot of rallies. I played good match against Svitolina. I think it's going to be a little bit similar to Simona. She beat her, so should be close. But I still have to play well. It's going to be difficult."