The world number one Serena Williams was dumped out of the Canadian Open semi-finals 3-6 7-5 6-4 by rising Swiss talent Belinda Bencic, who went on to beat Simona Halep in Monday's final.
Sunday's defeat was just the second in 45 matches this season for Williams, who has won the first three grand slams of the year and will be favourite for a fourth when the US Open kicks off at the end of the month.
The unseeded Bencic, who also beat former world number ones Caroline Wozniacki and Ana Ivanovic in Toronto, wore a look of disbelief after the 18-year-old's forehand winner whizzed past Williams to seal the match.
Bencic dropped her racket and covered her face with her hands before the tears started to flow after defeating Williams.
"I can't believe it now," said Bencic said. "The first set was just too fast for me, I think. But then I adapted to the game in the second set, and then I was just fighting. I mean I had 5-1 (in the third set). I'm so happy. It's amazing."
The next day, the Swiss teenager capped a brilliant run to the Rogers Cup title when distressed second seed Simona Halep retired from the final after losing the first three games of the third set.
Bencic needed nearly two hours and 30 minutes on a sweltering center court to see off a determined Halep 7-6 6-7 3-0 and claim the biggest title of her young career, putting down a marker as a player to watch at the upcoming US Open.