Kyrgios, the current world number 19, admitted he had “played pretty bad” after he was beaten 7-6, 3-6, 6-3 by the unfancied Shapovalov.

The 17-year-old, ranked 370 in the world and is competing in his maiden Association of Tennis Professionals (ATP) event, will next face Grigor Dmitrov.

The Bulgarian was pushed all the way by Yuichi Sigata of Japan as he dropped the opening set before he eventually progressed in three sets, 5-7, 7-6, 6-4.

“I'm not going to tell you what I did or didn't do to prepare,” Kyrgios said.

“I just played pretty bad.

“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.”

Elsewhere on day one of the Rogers Cup, part of the ATP Masters Series and is the last major competition on the calendar before next month's Olympic Games in Rio de Janeiro, Kyrgios’ compatriot Bernard Tomic safely reached round two by beating Alejandro González of Colombia.

Tomic, who has ruled himself out of Rio 2016, along with Kyrgios, enjoyed a comfortable outing as he prevailed with a 6-4, 7-6 success.

Elsewhere, Sam Querrey of the United States, the conqueror of world number one Novak Djokovic at Wimbledon, continued his good run of form with a 7-6, 6-4 win over Canada’s Frank Dancevic.

Querrey’s team-mate John Isner, the big-serving ninth seed, squeezed through to the second round as he recovered from a set down to beat Israel’s Dudi Sela, 4-6, 6-3, 6-2.

In the women’s tournament, Petra Kvitova of the Czech Republic made light work of Poland’s Magda Linette with a 6-1, 6-2 victory.

Australia’s Sam Stosur, the 13th seed, is also into the next round as she proved too strong for Britain’s Heather Watson, emerging with a 7-5, 6-3 win.

A number of the game’s top players, including Wimbledon champions Andy Murray and Serena Williams, have opted not to compete at the Rogers Cup to concentrate on Rio 2016.