Swiatek, ranked third in the world and seeded second in Montreal, followed top-seeded Coco Gauff, third-seeded two-time defending champion Jessica Pegula and fourth-seeded Mirra Andreeva out the door as Tauson booked a quarter-final berth against Australian Open champion Madison Keys.
Sixth-seeded Keys saved two match points on the way to a 4-6, 6-3, 7-5 victory over Czech Karolina Muchova – the American’s third match win of the year in which she overcame a match point.
Meanwhile, it was clear sailing for former world number one Naomi Osaka, who needed just 49 minutes to blast past Anastasija Sevastova 6-1, 6-0.
The second-quickest win of Osaka’s career put her into her first quarter-final at the 1000 or Grand Slam level since Doha in 2024.
Swiatek, playing her first tournament since winning her sixth Grand Slam title at the All England Club last month, looked out of sorts from the start on a breezy centre court.
She fell behind a quick break and failed to convert a pair of break chances in the eighth game as Tauson took a 5-3 lead in the first set.
The Polish star appeared to be finding her rhythm as she won the next three games to get her nose in front 6-5.
But Tauson, who won her first WTA title in New Zealand in January, held to force the tiebreaker and dominated, Swiatek surrendering the set with a double fault on the Dane’s first set point.
Swiatek had saved a pair of break points in the eighth game of the second set when another untimely double fault gave Tauson the break and a 5-3 lead.
Tauson calmly served it out, claiming her first win in four career meetings with Swiatek when the Pole belted a backhand into the net.
Tauson will be up against a battle-tested opponent in Keys, who saved two match points on her own serve in the 10th game of the third set, striping a forehand on the first and escaping the second as Czech Muchova misfired on a service return.
“I’m really happy to get that win,” Keys told the crowd. “After losing the first set and even being match point down, being able to figure it out – it’s always a great day.”
Osaka, who has struggled for consistency since returning from maternity leave in 2024, said the coaching shakeup she instigated this week – parting with Patrick Mouratoglou after less than a year and teaming up on a trial basis with former Swiatek coach Tomasz Wiktorowski – had energised her.
“I enjoy his coaching style. He’s very direct and to the point. For someone like me, who my thoughts scatter around often, it’s very helpful,” said Osaka, who lost in the first round of the French Open and the third round at Wimbledon and arrived in Montreal ranked 49th in the world.
She will face either fifth-seeded American Amanda Anisimova or Ukraine’s Elina Svitlina for a semi-final berth.
Anismimova is playing her first tournament since a runner-up finish to Swiatek at Wimbledon, where she admitted she was overwhelmed by nerves in a 6-0, 6-0 loss to the Polish star in the final. (AFP)