World number two Gauff clawed her way back from a set down to defeat Russian Veronika Kudermetova 4–6, 7–5, 6–2 in a match that stretched over two and a half hours.
Top seed Coco Gauff staged a thrilling comeback to reach the last 16 of the Canadian Open on Thursday, while former US Open champion Daniil Medvedev was knocked out of the men's tournament by Australian Alexei Popyrin.
World number two Gauff clawed her way back from a set down to defeat Russian Veronika Kudermetova 4–6, 7–5, 6–2 in a match that stretched over two and a half hours.
"It was a tough match today," the French Open champion said.
"I thought I did well mentally, especially on the return. I was playing an opponent who served really well. Obviously, I would have liked to serve better, but I'm just happy to get through."
Ukrainian Dayana Yastremska stunned American eighth seed Emma Navarro 7–5, 6–4 while Russian fourth seed Mirra Andreeva also exited the tournament, losing 7–6(5) 6–4 to American McCartney Kessler.
Ninth seed Elena Rybakina from Kazakhstan saw off Romanian Jaqueline Cristian 6–0 7–6(5).
On the men's side, Alex Michelsen toppled third seed Lorenzo Musetti 3–6, 7–6(4), 6–4 in a gripping third-round contest.
The American 26th seed shrugged off a sluggish start to unleash a barrage of big hitting and keep the Italian on the ropes.
The shocks kept coming as 10th seed Medvedev was stunned by 18th seed Popyrin 5–7, 6–4, 6–4, while German top seed Alexander Zverev had to come from a set down to defeat Italian Matteo Arnaldi 6-7(5), 6–3, 6–2 to claim his 500th tour-level match win.
Eighth seed Casper Ruud from Norway beat Portugal's Nuno Borges 7–5, 6–4, fifth seed Holger Rune cruised past Alexandre Muller 6–2, 6–4, and Francisco Cerundolo defeated his Argentine compatriot Tomas Etcheverry 6–3. 6–4.
