Pegula battles past Kostyuk at WTA Finals

Jessica Pegula reignited her challenge at the season-ending WTA Finals on Tuesday, battling past Ukraine's Marta Kostyuk in straight sets to stay on course for a semi-final berth.

Pegula, beaten by Coco Gauff in her opening group game at Indian Wells on Sunday, overcame a topsy-turvy second set to win 6-2, 7-5.

The win means Pegula can advance to the last four with a victory over Czech eighth seed Linda Noskova in her final group game. Kostyuk is eliminated following the defeat.

"I feel like I'm playing well," Pegula said. "I felt my match against Coco was a super high-level match and that was a great match today.

"It's so tricky with her because you just don't know what's gonna come -– she will just step in and inject pace, she'll come and kamikaze the net, she goes for returns or her serve can get hot. That's what makes it difficult to play her."

The 32-year-old American had looked in complete control in the first set, breaking Kostyuk in the first and seventh games to take the opener 6-2.

A chaotic second set began with four consecutive service breaks before Kostyuk held for a 3-2 lead.

The Ukrainian then had a break point in the next game but was unable to take advantage as Pegula held for 3-3.

The next four games went with serve but Pegula finally grabbed the decisive break in the 11th game. She converted her fourth break point to take a 6-5 lead before holding for the match, sealing victory when Kostyuk smacked a forehand long.