British number one Katie Boulter was swept aside in straight sets by American teenager Coco Gauff in the second round of the National Bank Open.
Boulter, 27, had not dropped a set in coming through two qualifying matches and her main-draw opener in Montreal.
But she lost 6-2 6-2 to 19-year-old Gauff, who will face Wimbledon champion Marketa Vondrousova in the last 16.
The Czech brought Caroline Wozniacki's comeback tournament to an end, beating the former world number one 6-2 7-5.
Wozniacki lost serve twice in a one-sided opening set but recovered from a double break down at 3-0 in the second, only to crucially drop serve again at 5-5 before Vondrousova served out the match.
Earlier Gauff, ranked seventh in the world, made a blistering start against Boulter on Wednesday as she lost just three points in the first four games of the opening set, twice breaking serve to establish a 4-0 lead.
World number 72 Boulter responded with a break of her own and later saved two set points at 5-2 and 40-0 down but Gauff converted the third.
The Briton failed to take a break point at the beginning of the second set and was broken three games later before Gauff sealed victory with another break, despite Boulter saving three match points.
Elsewhere, Poland's world number one Iga Swiatek was given a first-set scare by the Czech Republic's Karolina Pliskova before progressing 7-6 (8-6) 6-2, while fourth seed Jessica Pegula beat Yulia Putintseva 6-4 6-4.
Fifth seed Caroline Garcia of France was upset 6-4 4-6 6-2 by Czech Marie Bouzkova, while Sloane Stephens enjoyed a walkover into round three after Victoria Azarenka's withdrawal through injury.
World number three Elena Rybakina came from a set down to beat the United States' Jennifer Brady 6-7 (3-7) 7-6 (7-5) 6-3 in a match held over from Tuesday night because of rain.
