Daria Saville has scored a highly impressive straight-sets win over Jessica Pegula to book her place in the quarter-finals of the WTA event in Washington.

Having beaten Swede Mirjam Bjorklund in three sets to open her campaign, a resurgent Saville saw off the No.1 seed and defending champion 7-5 6-4 in 98 minutes for her second top-10 win of the season.

The Australian will face Rebecca Marino in the last eight after the 31-year-old Canadian defeated Germany's Andrea Petkovic 6-3 3-6 6-1.

"I was really excited to play against a top-10 player again," Saville said.

"It was a great challenge. To get away with a win is even better.

"I feel like I'm playing really good tennis right now. I'm excited for more."

Elsewhere on Wednesday, former world No.1 and third seed Simona Halep retired in the second set of her match against Russia's Anna Kalinskaya because of illness when trailing 5-7 0-2.

Kalinskaya will face sixth seed Kaia Kanepi in the last eight after the Estonian defeated China's Zhu Lin 4-6 6-4 6-4.

In the first meeting between Saville and Pegula, it started to go wrong for the American in the ninth game of the opening set as Saville broke to love.

Pegula, who won her first WTA singles title at the most recent edition of the Citi Open in 2019, immediately broke back before dropping her serve again. Saville closed it out at her second opportunity.

The Aussie broke serve in the first game of the second set and after Pegula had six break-back chances over the remainder of the match, Saville saved every one to close out the win.

Saville is now into her third quarter-final of the year, all on hard courts, after Miami and Guadalajara.

The 28-year-old was ranked as low as world No.627 as recently as February this year, following Achilles tendon surgery which kept her out of action for almost the entire 2021 season.

But she has charged back up to world No.88, also bolstered by a round-of-16 showing at Indian Wells where she beat world No.5 and Wimbledon finalist Ons Jabeur.

With AP.