Canada's Bianca Andreescu was eliminated from the WTA Finals on Wednesday after retiring from her match against Karolina Pliskova with a left knee injury.

Andreescu was leading 2-0 in the first set, with Pliskova serving at 15-15 in the third game, when she came up limping after returning a serve and took a long medical timeout.

She had her knee taped and she played through the first set, even challenging Pliskova's serve with three break-point opportunities in the fifth game, but clearly struggled with her movement and retired after losing the set 6-3. Pliskova won on an ace that Andreescu didn't move to return.

"I stepped weirdly on a return," Andreescu said after the match in Shenzhen, China. "I heard my knee crack. It kind of went inwards. Putting pressure afterwards on it really bothered me. I could barely bend my knee.

WATCH | Andreescu injures knee in 1st set:

Bianca Andreescu of Mississauga, Ont., injured her left knee while returning a serve in her WTA Finals match against Karolina Pliskova of the Czech Republic. Andreescu would later retire from the match. 1:50

MRI on Thursday

"But I fought with the pain as much as I could. At some point an athlete has to say 'stop' and just listen to their body. That's what I did."

Andreescu called for coach Sylvain Bruneau after going down 3-2 and told him she was having trouble bending her knee. He told her not to push it. A visibly upset Andreescu said: "I don't want to stop."

WATCH: Bianca Andreescu: 'I can't bend my knee'

Despite injuring her left knee, Bianca Andreescu vowed to carry on during the first round of her WTA Finals match against Karolina Pliskova. 0:40

Andreescu said she will get an MRI on Thursday to determine the extent of the injury.

Pliskova said she felt "sorry" for Andreescu, but otherwise offered little sympathy for her opponent.

"I don't know how bad it is," the No. 2 seed said of Andreescu's injury after the match. "I was just ready that she was going to call physio because so far I think she has been calling physio in every match. It was not really a surprise for me."

"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," Pliskova added.

The 19-year-old from Mississauga, Ont., is now 0-2 at the season-ending, $14-million US event and can't advance to the semifinals.

Pliskova, who lost to Andreescu in three sets in the Rogers Cup quarter-finals in August, will play Simona Halep for a semifinal spot. Halep defeated Andreescu in their opening match on Monday.

It's been amazing. I made history in Canada. I won my first [Grand] Slam. My game just keeps getting better and better. — Canada's Bianca Andreescu on her 2019 breakthrough season

Andreescu said after the Halep match that she was having trouble with her back, but the pain cleared up after treatment.

Despite the disappointment of an injury-plagued finish, Andreescu's breakout 2019 season — highlighted by a win over Serena Williams in the U.S. Open final to become the first Canadian to win a Grand Slam singles title — was overwhelmingly positive.

"It's been amazing. I really can't complain," she said. "I made history in Canada. I won my first slam. My game just keeps getting better and better. The thing with me, though, is that I'm never satisfied. Even looking back at that, I still want to do well right now.

"But I have to look at the positives. Hopefully I can recover quick after this. Who knows if I can play. We'll see. If not, then I'm going to have a good pre-season, good off-season, be ready for 2020."

17-match win streak

Andreescu, the world No. 4 ahead of her debut at the season-ending WTA Finals, arrived in Shenzhen with a 48-5 season record and coming off a quarter-final loss to Naomi Osaka at the China Open earlier this month.

She was attempting to complete a sensational season with a fourth title following other victories at Indian Wells and Rogers Cup.

WATCH | Bianca Andreescu exits match early with knee injury:

Bianca Andreescu of Mississauga, Ont., retired from her WTA Finals match due to injury, after dropping the first set 6-3 to Karolina Pliskova of the Czech Republic. 1:00

The loss to Osaka was Andreescu's first on the Tour in six months not counting withdrawals and retirements and halted a 17-match win streak that saw the resident of Thornhill, Ont., soar up the WTA rankings.

Andreescu, who opened 2019 ranked outside the top 150, was the first Canadian to play in the WTA Finals since Eugenie Bouchard in 2014.

Osaka, a two-time Grand Slam champion, withdrew from the WTA Finals on Tuesday with a right shoulder injury.

Svitolina advances to semis

Earlier Wednesday, defending champion Elina Svitolina qualified for the semifinals by beating Halep 7-5, 6-3.

Svitolina, the only competitor in the eight-player field not to win a title this season, last won a tournament at last year's WTA Finals.

Whoa! 😮Crazy spin on <a href="https://twitter.com/ElinaSvitolina?ref_src=twsrc%5Etfw">@ElinaSvitolina</a> forehand winner<a href="https://twitter.com/hashtag/WTAFinals?src=hash&ref_src=twsrc%5Etfw">#WTAFinals</a> <a href="https://t.co/sqtROOuYrG">pic.twitter.com/sqtROOuYrG</a> —@WTA

The Ukrainian is 2-0 in the Purple Group, winning both of her matches in straight sets. Halep is 1-1.

Svitolina broke Halep in the final game of the first set to take the lead. She then broke the Romanian's serve in the eighth game of the second set and held to win.

The victory was Svitolina's fifth in nine matches against Halep. On the four previous occasions in which she won, Svitolina went on to win the tournament.