Toronto - Nick Kyrgios turned in a patchy performance to exit the Toronto Masters 7-6 (7/2), 3-6, 6-3 on Monday at the hands of Wimbledon junior winner Denis Shapovalov.
The 17-year-old Canadian set up a match point with his 12th ace, then calmly closed out the upset over the 19th-ranked Australian.
In his first match since losing to eventual champion Andy Murray in the Wimbledon fourth round, Kyrgios at times showed little interest in his on-court duties, serving at lightning speed with only a few seconds between points.
During one changeover, he was heard muttering to himself in dissatisfaction.
The Australian 11th seed somehow struck an ace as his racquet flew from his hand on one serve; he also double-faulted 18 times while managing 13 aces.
Shapovalov, playing in only his second ATP event, will take on former top 10 contender Grigor Dimitrov, who is trying to claw his way back in what has been a disappointing season.
The Bulgarian reached the second round with a 5-7, 7-6 (7/5), 6-4 win over Yuichi Sugita.
Three other seeds advanced, with number nine John Isner coming back to eliminate Dudi Sela 4-6, 6-3, 6-2.
Australian 12th seed Bernard Tomic beat Alejandro Gonzalez 6-4, 7-6 (7/0) while Jack Sock, the number 16, defeated Denis Kudla 6-2, 6-2.
Dimitrov, ranked 48th, got out of danger against Sugita after trailing a set and a break.
Dimitrov, who lost six straight matches prior to Wimbledon, improved to 21-16 in 2016.
"It was a very tough match, I didn't play my best tennis but I got through. It was great to hear some Bulgarian voices in the crowd when I got down on myself," he said.
"The weeks before Wimbledon were difficult for me," he added. "I was still working hard, trying to perform.
"Patience is the key for me now, that's what it's all about."
Dimitrov said he finally turned the corner in the match while trailing 4-1 in the second-set tiebreaker, standing just a handful of points from a first-round exit.
The Bulgarian won a lob-to-lob exchange with the 107th-ranked Sugita, coming through to eventually level the set and take on new life in the third.
"I was desperate to win that point," Dimitrov admitted. "It feels great to win a round here."
Borna Coric won an all-Croatian clash as he beat Ivan Dodig 5-7, 6-4, 6-2.
"It was a good match from my side," said the winner, who next plays fifth seeded Czech Tomas Berdych. "In the first set, I didn't play my best tennis and I didn't feel very confident.
"I got a little bit angry, but in the end it was good because I needed to let it out of my system."
South African Kevin Anderson ended a losing streak of three consecutive opening matches, downing Serb Viktor Troicki 7-6 (7/4), 6-3.
Canadian Steven Diez surprised Briton Kyle Edmund 3-6, 6-3, 6-2. The wild card entry will play Tomic.
Results on Monday in the Toronto ATP Masters hardcourt tennis tournament (x-denotes seeded player):
Borna Coric (CRO) bt Ivan Dodig (CRO) 5-7, 6-4, 6-2
Kevin Anderson (RSA) bt Viktor Troicki (SRB) 7-6 (7/4), 6-3
Steven Diez (CAN) bt Kyle Edmund (GBR) 3-6, 6-3, 6-2
Gilles Muller (LUX) bt Dmitry Tursunov (RUS) 7-6 (7/5), 6-1
Peter Polansky (CAN) bt Tim Smyczek (USA) 4-6, 6-3, 6-0
Ryan Harrison (USA) bt Andrey Kuznetsov (RUS) 6-3, 6-1
Grigor Dimitrov (BUL) bt Yuichi Sugita (JPN) 5-7, 7-6 (7/5), 6-4
John Isner (USA x9) bt Dudi Sela (ISR) 4-6, 6-3, 6-2
Bernard Tomic (AUS x12) bt Alejandro Gonzlez (COL) 6-4, 7-6 (7/1)
Jack Sock (USA x16) bt Denis Kudla (USA) 6-2, 6-2
Mikhail Youzhny (RUS) bt Stephane Robert (FRA) 6-3, 7-6 (8/6)
Denis Shapovalov (CAN) bt Nick Kyrgios (AUS) 7-6 (7/2), 3-6, 6-3