Rafael Nadal is out of the Rogers Cup after a shock second round defeat against Croatia's Ivan Dodig.
The Spaniard, playing for the first time since losing to Novak Djokovic in the Wimbledon final in July, won the opening set 6-1.
However, Dodig hit back to take the next two sets, both on tie-breaks, and clinch the match 1-6 7-6 7-6.
Two-time winner Roger Federer reached the last 16 with a 7-5 6-3 win over Canadian Vasek Pospisil.
Dodig, who hit 19 aces in all, will play Janko Tipsarevic for a place in the quarter-finals.
"This is the greatest moment of my life," said Dodig who is ranked 41 in the world.
Nadal, winner of the Canadian event in 2005 and 2008, said: "He played very well, very aggressive.
"He didn't feel the pressure in the important moments. And at the end of the match, probably I was a little bit unlucky today, no?"
Federer, who lost in last year's Montreal final to Andy Murray, broke his opponent once in each set serving four aces in total.
The 16-time Grand Slam champion will now play Jo-Wilfried Tsonga for a place in the quarter-finals.
Frenchman Tsonga, who beat Federer in an enthralling five-set epic in the quarter-finals at Wimbledon in June, beat Australian Bernard Tomic 6-3 7-6 (7-1).
Djokovic, the 2007 Rogers Cup champion, had to survive a scare before beating 30th-ranked Nikolay Davydenko of Russia 7-5 6-1 to improve his stunning 2011 winning record to 49-1 overall and 25-0 on hard courts.
Andy Murray put his singles' exit behind him as he teamed up with brother Jamie in the doubles event - the Scottish pair beat Canadians Eric Chvojka and Pierre-Ludovic Duclos in a final set champions tie-break.
The Murrays won the first set 6-2, then lost the second set by the same score. They won the deciding champions tie-break 10-7.