The American fired a serve up the T that Svitolina could not handle to end the high-quality contest and its riveting 54-minute third set.

Svitolina, who returned from maternity break in April and made the semi-finals of Wimbledon last month, dug deep to fend off two match points in her final service game but was unable to convert her break point opportunities in the deciding set.

Svitolina has produced stunning results including a win over world number one Iga Swiatek at the All England Club in July despite the turmoil caused by Russia's invasion of Ukraine.

"I have tons of respect for her," Pegula said in an on-court interview.

"She just had a baby, and with everything she is going through with her country, I told her I feel like she came back as a new person. I can see the competitiveness in her and I've always really respected that."

Pegula, who won the WTA 500 event in 2019, improved to 3-1 lifetime against wildcard Svitolina and will next face either Greece's Maria Sakkari or American Madison Keys, who play their quarter-final later on Friday.