SINGAPORE - Elina Svitolina endured an emotional evening to kick off action at the BNP Paribas WTA Finals Singapore presented by SC Global, reversing a 1-7 head-to-head against Petra Kvitova despite feeling under the weather in press on Sunday.

Read more: 'I was preparing to play Zhuhai' - Svitolina making most of WTA Finals return

"I'm just not feeling good," a red-eyed Ukrainian admitted after taking a short break to recover from what was desribed as a sudden bout of light-headedness.

Moments earlier, Svitolina had sounded confident about her chances to make the semifinals in her second WTA Finals appearance, dropping serve just once to end Kvitova's streak of 12 straight sets won against her in under 90 minutes.

"I want to take this win as one to go forward, and for all those people and haters that were saying, you know, that I don't deserve to be here and I'm, you know, not good."

- Elina Svitolina

"I was playing good today, you know, quite solid from the baseline and putting pressure on Petra today. This was the key for me."

Svitolina narrowly missed out on a chance to make it out of round robin play last year, shocking World No.1 Simona Halep but losing a tight three-setter to eventual semifinalist Caroline Garcia. During All Access Hour on Saturday, the former World No.3 had been candid about not knowing whether she'd ultimately qualify for Singapore, a decision that came down to results at the VTB Kremlin Cup just last week. 

Fresh off a statement win over a two-time Wimbledon champion, Svitolina initially struck a defiant pose, dedicating tonight's win to her doubters.

"Winning this match definitely gives me lots of confidence. I want to take this as one to go forward, and for all those people and haters that were saying that I don't deserve to be here and I'm, you know, not good.

"Until the next match, I can really enjoy this win."

Following the timeout, she nonetheless noted the challenges her group posed, with former No.1 Karolina Pliskova looming as her next opponent.

"It's not going to get harder and harder. It's already very, very hard, each match. I already had the match today which was extremely hard for me, because I lost seven times against her. So, I mean, you couldn't ask for a harder start, I think.

"So it's going to be good match next match. I will just try to recover and be ready for next one and I have to be ready for anything and just fight, because it's round robin, so you don't know until the very end."

Svitolina will face Pliskova on Tuesday night.