Andy Murray was sent crashing out of the Rogers Cup in Montreal after a 6-4 6-3 third-round defeat to Ernests Gulbis.
The British No 1, playing in his first tournament since becoming Wimbledon champion, was second best throughout as his Latvian opponent recorded one of the best results of his career.
Murray had won 13 matches in a row going into the contest but has now seen that run come to an end after Gulbis completed the victory in an hour and 28 minutes.
"I wouldn't say that I played my best tennis," Gulbis told Sky Sports after the match.
"I played a very solid game and a very good game but I am still struggling with my feeling and I'm getting better match by match. I hope I'll be even better tomorrow."
Gulbis, who has long been touted as a player who has not yet lived up to his potential, added: "I was ranked 150 coming into this year.
"I skipped Australia, I couldn't get a wildcard in a challenger main draw. I've been struggling - up and down. Now I am slowly but I think surely going back to where I belong in the rankings.
"I want to crack the top 20 and from there, one or two big wins and you're there in the top 10. So I'm looking forward to it."
Murray had Gulbis at 15-40 in the seventh game but the Latvian, who is currently ranked No 38 in the world, did well hold on to his serve and take a 4-3 lead.
The first set continued on serve until Murray's game let him down and Gulbis found himself with three set points, the second of which he converted.
Gulbis broke Murray's serve again early in the second set to take a 3-1 lead but the world No 2 hit back immediately to seal his first break of the match after a brilliant rally.
However, it proved to be a brief respite as Gulbis struck again to claim a 5-3 lead, leaving him to serve it out to complete the shock win.