SINGAPORE - No.6 seed Elina Svitolina powered through a tough encounter with No.7 Karolina Pliskova, edging through in three sets to claim the top spot in the White Group at the BNP Paribas WTA Finals Singapore presented by SC Global.

Svitolina posted a strong service game to take down the WTA Ace Queen, firing eight aces and needed an hour and 54 minutes to seal the 6-3, 2-6, 6-3 victory.

Read more: WTA Finals 2018 Live Blog: Second Singapore success for Svitolina

“My goal was to make an extra ball over the net and fight until the very end and for every point, to don't give any easy errors,” Svitolina said in her post-match press conference. “I think this was the key today. It worked really good, because I think Karolina was up and down and struggling sometimes with her serve. I had to be ready to take my chances. That's why I'm very happy with that.

“It was a really challenging opening match, and this one, as well, so I'm very happy that I could handle those two, and I still have my next match very, very tough and, you know, I'm looking forward to it.”

After opening her round robin campaign with a straight sets win over Petra Kvitova, Svitolina had a chance to claim a semifinal spot with another two-set win today. But Pliskova had other ideas, pushing the Ukrainian to three to ensure that the White Group winners will be decided on Thursday, the final day of group stage action.

The match was a hard-fought affair from start to finish, with both players dialled in and gunning for the first semifinal spot. Svitolina found herself having to battle through a marathon 15-minute game in the third game of the set, fighting off six of Pliskova’s break chances to keep them on serve.

The Ukrainian finally broke through the rock-solid Pliskova serve at 4-3, staying aggressive to reel off the next two games in a row. She faced a bit of a hiccup as she served it out, with Pliskova looking keen to send them into a decider, but a timely ace sealed the set point. Pliskova will likely rue her missed opportunities in the first set - she was unable to convert on any of her eight break chances in total.

But Pliskova didn’t let it get to her, and instead she raised her level in the second set as her powerful serve started to click. She served out two love games in a row, putting all the pressure on Svitolina. The Ukrainian finally caved at 4-2, and Pliskova raced ahead to lead 4-2, staying aggressive to take the set and keep Svitolina out of the rallies.

Svitolina was back on track in the deciding set, covering the court and reeling off back-to-back breaks of serve to create a daunting 4-0 lead against Pliskova. The Czech fought to stay in the match, breaking Svitolina twice - but both times Svitolina broke straight back to reestablish her three-game lead. After a tug-of-war last few games, it was Svitolina who emerged victorious, recording her second Singapore win just as the clock ticked past midnight.

Svitolina stayed solid against the Pliskova attack, recording 29 winners and just 18 unforced errors across the three sets, compared to the Czech’s 33 and 28. She struck eight aces to Pliskova’s six, and edged ahead in break point success: she converted five of her 13 chances while Pliskova only four of 14.

“I think my serve was not great today at all, but it's also, on the other hand, she's returning pretty well, so she's putting a lot of balls back,” Pliskova told reporters afterwards. “So there is the pressure that you always have to play the ball after the serve.

“I think the second set was overall I think maybe one of the best sets what I played this year. So pretty positive about that. Obviously the third set I didn't hold much my serve, which is always frustrating, but she's a good player, too, so I was not there alone.”

Despite winning both of her round robin matches, Svitolina dropping a set today ensures that she can’t advance to the semifinals until at least Thursday, the last day of White Group play. Svitolina will face Wozniacki in her next match - she has to win at least one set to advance to the semifinals.

“I'm not gonna think about [the semifinals] going into the next match, because I don't want to have this kind of thing in my head,” Svitolina said. “I have to play my next match.

“[Against Wozniacki] it’s another tough battle. She's a fighter and so am I. It's gonna be a tough match, you know. There is no easy matches here, so, you know, recover, practice - and here you go again, playing on Thursday.”

As it stands, Svitolina tops the group with 2 wins and 0 losses (4-1 sets), and Pliskova and Caroline Wozniacki are both tied at 1-1, with Pliskova claiming the No.2 spot due to the sets differential (she won 3 sets and lost 2, while Wozniacki won 2 sets and lost 3). Meanwhile, Kvitova rounds out the group, taking the No.4 spot with a 0-2 record.