World number 19 Nick Kyrgios suffered a shock defeat by Wimbledon junior champion Denis Shapovalov in the first round of the Rogers Cup in Toronto.
He was beaten 7-6 (7-2) 3-6 6-3 in his first match since losing to eventual champion Andy Murray at Wimbledon.
"I'm not going to tell you what I did or didn't do to prepare. I just played pretty bad," said the Australian, 21.
Canadian Shapovalov, 17, is competing in only his second ATP event, and plays Bulgarian Grigor Dimitrov next.
Ranked 370 in the world, Shapovalov struck 12 aces in the match against an off-key Kyrgios, who served 18 double faults.
The Australian added: "He played great and he earned it. Obviously he was excited playing in front of his home crowd.
"I know what it feels like to come off one of your biggest junior results and then play in one of your home tournaments."