Coco Gauff falls to Shnaider as Aryna Sabalenka advances to quarterfinals in Toronto

Boulter pushed the world number three at multiple stages in the match, creating four break point opportunities, but she was unable to capitalise on them, ultimately going down 6-3 6-3.

Sabalenka will face American Amanda Anisimova in the quarter-finals, which will feature five American players.

Anisimova advanced to the last eight when No 10 seed Anna Kalinskaya retired with an injury after dropping the first set 6-2.

Asked about missing out on the Olympics, Anisimova said: "That kind of sucks, but it also makes me proud of my country. There's a lot of American top players that are playing amazing right now. It's a super-strong team that we have."

Top-seeded American Coco Gauff is not one of the Americans in the quarterfinals, after she was upset 6-4 6-1 by fellow 20-year-old Diana Shnaider.

It marked the Russian's first career victory over a top 10 player.

"Sometimes I question like whether I should have played or not," said Gauff, who just returned from the Olympics, "but at the end of the day I wanted to test myself and see if I would be able to, how I would do being mentally tired a little bit and physically fatigued.

The world number 24 Shnaider will take on sixth seed Liudmila Samsonova in the quarter-finals.

READ MORE: Mine de Klerk reflects on her Olympic Games debut in Paris