Teenage world number 370 Denis Shapovalov stunned Nick Kyrgios in the Rogers Cup first round on Monday.
The 17-year-old Canadian wildcard beat the Australian 11th seed 7-6 (7-2) 3-6 6-3 at the ATP 1000 event in Toronto.
Shapovalov, the Wimbledon junior champion, mixed 37 winners with 34 unforced errors in his surprise win.
Kyrgios ended up with 44 unforced errors and 18 double faults, losing in one hour, 39 minutes.
Shapovalov broke in the second game of the deciding set on his way to a 3-0 lead he would not relinquish.
He will face Bulgarian Grigor Dimitrov in the second round.