In a third-round battle of 20-year-olds, Russia's Diana Shnaider upset top-seeded Coco Gauff of the United States 6-4, 6-1 on Friday to advance to the quarterfinals of the National Bank Open in Toronto.

Shnaider, the 14th seed, has never advanced past the third round of a Grand Slam tournament. Gauff will defend her U.S. Open championship later this month.

Shnaider won 81 percent of her first-serve points and saved the only break point she faced. She closed the match emphatically by winning the last five games as she beat a top-10-ranked opponent for the first time.

"I mean, I tried to play it cool, but inside I was like, 'Yes! I made it!'" Shnaider said of the victory.

She moves on to oppose Russian countrywoman Liudmila Samsonova, the sixth seed, who cruised to a 6-2, 6-4 victory over Belgium's Elise Mertens.

Second-seeded Aryna Sabalenka of Belarus rolled past Great Britain's Katie Boulter 6-3, 6-3.

Lucky loser Taylor Townsend put on a solid performance while routing No. 4 seed Jelena Ostapenko 6-2, 6-1.

Townsend had five aces and 15 winners while putting away Ostapenko in just 60 minutes.

Townsend initially lost in qualifying before gaining a spot in the main draw when Yulia Putintseva of Kazakhstan withdrew due to the knee injury that prevented her from playing in the Paris Olympics.

The schedule was delayed Friday due to rain and Townsend arrived for the match with Ostapenko with just six minutes to spare.

"I just did two bike sprints, and I said, 'Let's go!,'" Townsend said. "I guess you've just got to get lucky every once in a while. The day that I found out I was playing as a lucky loser, I got here at 8:30 in the morning, and I found out I was playing not before 5 p.m.

"Those type of days, where you have to go and play and just figure things out, I think it really works well for me. I'm just trusting the work that I'm putting in, and I'm having fun. I'm having a great time, and I'm just riding this wave."

Townsend committed just eight unforced errors while Ostapenko from Latvia racked up 27.

Townsend will face fellow American Emma Navarro on Saturday. The eighth-seeded Navarro recorded a 7-5, 7-5 victory over No. 11 Marta Kostyuk of Ukraine.

Third-seeded Jessica Pegula notched a 6-2, 6-4 win over Ashlyn Krueger in a battle of Americans.

Pegula took advantage of Krueger's nine double faults while earning a quarterfinal date with American Peyton Stearns, who beat 12th-seeded Victoria Azarenka 6-4, 4-2. Azarenka retired due to a leg injury.

Amanda Anisimova also moved on, winning the first set 6-2 before No. 10 seed Anna Kalinskaya of Russia retired with an undisclosed injury.

--Field Level Media