Women’s world number one Aryna Sabalenka suffered a surprise defeat in the Canadian Open weeks before she begins her US Open title defence, while Britain’s Cameron Norrie also bowed out in the last 16.
Sabalenka lost 7-6 (7-3) 4-6 6-4 to Russia’s Ekaterina Alexandrova in a match lasting almost two and a half hours in Toronto.
The Belarusian recovered from a set down to force a decider, but a double fault when serving to stay in the match handed the number 16 seed victory.
It is the latest defeat in what has been a difficult summer for Sabalenka, who was knocked out in the quarter-finals and last 16 of the French Open and Wimbledon respectively.
“I just tried to play every single point as if it was the last one because with her, you don’t [get] a lot of chances during the match,” Alexandrova said.
“I’m super happy that I could win because after the second set, I thought [the chance] was already past me.”
The Russian will face Ukraine’s Elina Svitolina for a place in the semi-finals, after she defeated American eighth seed Amanda Anisimova 6-2 6-4.
Third seed Jessica Pegula suffered a first career loss to Diana Shnaider, as the 22-year-old finished both sets strongly to win 6-3 6-3.
The Russian will face Iga Swiatek in the semi-finals, after the seventh seed overcame opening set service troubles to defeat 10th seed Marta Kostyuk 3-6 6-1 6-2.
The six-time Grand Slam winner retired to the locker room after Kostyuk broke her serve four times during a shambolic a 39-minute opening set, but looked much improved when she returned.
In the men’s event in Montreal, British number two Cameron Norrie spurned two set-point opportunities as he was defeated 6-2 7-6 (10-8) by 18th seed Arthur Fils.
Norrie saved three match points in the second set to force a tie-break, but the Frenchman broke his serve to win in one hour and 43 minutes.
Fils will meet Spanish teenager Rafael Jodar in the quarter-finals, after the 19-year-old upset eighth seed Jiri Lehecka 6-3 6-3.
Brandon Nakashima and Luciano Darderi also progressed to the next round with gruelling three-set victories over Arthur Rinderknech and Nuno Borges respectively.
Italian Darderi used a mid-match changeover to enjoy an espresso as he battled to a 4-6 6-3 7-5 win.