In first three-setter between them, Jessica Pegula edges Coco Gauff in Montreal

WATCH: Jessica Pegula defeated Coco Gauff in three sets to reach the semifinals in Montreal.

While there are no secrets, on the court or off, between doubles partners Coco Gauff and Jessica Pegula, Friday's third-round match between the two at the Omnium Banque Nationale was uncharted territory.

For the first time, the Americans played a three-set match, and for the second time, Pegula emerged the victor: In two hours and 21 minutes, the elder of the two compatriots was a 6-2, 5-7, 7-5 winner—snapping Gauff's six-match winning streak and reaching the semifinals in Canada for the third year in a row.

Coming into the match, the first all-American quarterfinal in Canada in 22 years, something had to give: Gauff had won her last three matches against Top 10 players, including against Maria Sakkari to win the Mubadala Citi DC Open last week, and Pegula had lost her last four.

And when the final set went from 4-2 in Pegula's favor to 5-4 in Gauff's, Pegula could've been worried that she was in for some of the same. But the fourth seed steadied, and took advantage of some wobbles from Gauff at crucial moments; the sixth seed hit 59 unforced errors and double-faulted nine times, including twice on break point in the decider.

“That was a good match,” Pegula said afterwards in her on-court interview. “It’s always tough to play your doubles partner—you know exactly what you’re trying to do. It just came down to the wire and who was going to compete better.”

Pegula is through to her eighth career semifinal at a WTA 1000 event, all since 2021. She's also just the sixth player in the Open Era to reach the final four in each of her first three trips to Canada after Evonne Goolagong, Stefanie Graf, Monica Seles, Arantxa Sanchez Vicario and Chris Evert.