Stefanos Tsitsipas of Greece stunned Novak Djokovic with a three-set victory to end the Wimbledon champion's pursuit of a fifth Rogers Cup crown in Toronto.
Tsitsipas, the world number 27, secured his place in his first Association of Tennis Professionals Masters 1000 quarter-final with a shock 6-3, 6-7, 6-3 win at the Aviva Centre.
The result for the Greek player saw him knock out a seed for the second round in a row.
Tsitsipas had beaten seventh seed Dominic Thiem to set up a meeting with Djokovic, the ninth seed, but said his triumph over the former world number one was the best of his career.
"I knew I was playing pretty good today," he said.
"Losing the second set, it was tough to deal with - I had my opportunities and didn’t use them.
"But I remained calm, I tried few things that I didn’t try before.
"The early break in the third set was everything.
"It gave me the win at the end."
Tsitsipas is next due to play defending champion and second seed Alexander Zverev for a place in the semi-finals after the German comfortably dispatched Daniil Medvedev 6-3, 6-2 in just 52 minutes.
Top seed Rafael Nadal is also through after he overcame Switzerland's Stanislas Wawrinka 7-5, 7-6 in a battle of Grand Slam champions.
Nadal is next scheduled to face Croatian Marin Cilic, who beat Argentina's Diego Schwartzman 6-3, 6-2.
In the women's singles tournament at the IGA Stadium in Montréal, sixth seed Caroline Garcia recorded an impressive victory over Russia's Maria Sharapova to reach the next round.
Garcia proved too strong for Sharapova with a 6-3, 6-2 win and will take on top seed Simona Halep of Romania in the quarter-finals of the Women's Tennis Association Premier 5 tournament.
Second seed Caroline Wozniacki of Denmark also crashed out after she lost 5-7, 6-2, 7-6 to Belarus' Aryna Sabalenka.
The tournament in the two Canadian cities is due to continue tomorrow.