Svitolina returned at the Charleston Open in April following the birth of her daughter with fellow tennis player Gael Monfils and has produced stunning results despite the turmoil caused by Russia's invasion of Ukraine.
Pegula, from the United States, has beaten former world number three Svitolina twice in three previous meetings.
But she expects a tough challenge against the fierce 28-year-old who made the Wimbledon semi-finals last month having reached the French Open quarter-finals in June.
"It's going be a different match probably than the previous times I've played her," Pegula told reporters.
"I can tell from watching her matches, I feel she has a new perspective. So many things going on in her life."
Pegula received a bye in the Washington first round and beat Peyton Stearns 6-3 6-4 on Thursday, while Svitolina has taken out fifth seed Daria Kasatkina and former Grand Slam champion Victoria Azarenka.
"She's come back and reset nicely. She's been competing really well and playing very fearless," Pegula added.
"We'll see. It's going to be a tough match. She's been playing at a high level and I feel like she hasn't really missed a beat coming back."
Pegula, who has won titles in doubles alongside fellow American Coco Gauff this year, is chasing her third singles crown and first of 2023 following last season's triumph in Guadalajara.
The 29-year-old is no stranger to success in the U.S. capital having won her maiden title there in 2019.
"I won my first title here with my coach in our first week together and since then we've just been rising and it's been an awesome journey," Pegula said on the WTA website.
"That was a big turning point for me."
