Pegula, the defending champion of the tournament that serves as a hard-court tuneup for the US Open, lost 7-5, 6-4, with a spot in the quarterfinals on the line. The Buffalo, New York, native who's ranked seventh in the world won in Washington the last time the WTA played there in 2019 and was coming off reaching the round of 32 at Wimbledon this year.
"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," Saville said. "I'm excited for more."
On the men's side, Wimbledon runner-up Nick Kyrgios moved on by beating 14th-seeded Tommy Paul 6-3, 6-4. In his first singles tournament since reaching the final at the All-England Club, Kyrgios continued interacting with fans, checking on one who was struck by an errant ball and giving her a towel.
Kyrgios asked another fan where to serve from for match point Monday, a tradition he started when he won this tournament in 2019.
American Sebastian Korda knocked off 12th-seeded Sebastian Baez 6-1, 6-4, and ninth-seeded Holger Rune beat Benoit Paire 6-3, 6-2. Mikael Ymer, who started the tournament with a victory against Andy Murray, continued his run by defeating 15th-seeded Aslan Karatsev 6-4, 3-6, 6-4.
After bowing out of the US Open each of the past two years -- a loss to Denis Shapovalov in 2020 and then because of food poisoning in 2021 -- Korda is hoping rest helps him win his first singles match in the main draw of the Grand Slam.
"This year is going to be my first [time being] well-prepared [going] into the US Open -- just kind of taking a little break getting ready for the American hard-court swing and just hopefully just enjoy it," Korda said.