Gael Monfils missed squandered four match points in blistering heat before exiting in the first round of the ATP Toronto Masters on Sunday, losing 6-4, 4-6, 7-6 (7/3)to qualifier Tomas Barrios Vera.
French showman Monfils had his four winning chances in a pair of third-set service games against the Chilean who won his first match at Masters level while ending a seven-match losing streak dating to late February.
The pair both struggled in 35 Celsius summer temperatures, with number 142 Barrios Vera winning after nearly three hours on court.
Monfils struck a record 15 double-faults, the most ever recorded by the 38-year-old in a best-of-three match.
Barrios Vera moved into a second-round match against American Alex Michelsen.
"I don't know how I saved so many match points," the 27-year-old winner said. "It was super-close, super-tight.
"I tried to fight for every point, tried to serve well.
"This victory is very important for my confidence playing this type of (big) event."
Monfils, who also lost in the Canadian first round a year ago, rallied from a set and a break down as he competed for the 14th time in Canada but was unable to get over the line for victory.
He broke the Chilean twice in the second set to level the match but came undone in the third.
The 2016 and 2019 semifinalist, struggling with the heat as early as the third game of the afternoon, got back into contention as Barrios Vera double-faulted and lost his second-set momentum.
The Frenchman leaned heavily on his racquet between points as he looked to be struggling with his fitness as he tried in vain to close out the win.
He ended with 30 winners and 47 unforced errors while Barrios Vera had nearly 60 unforced errors in victory.
Elsewhere on opening day Reilly Opelka of the United States defeated Austrian Stefan Ofner 7-6 (8/6), 7-5 while France's Giovanni Mpetshi Perricard advanced past Japanese qualifier Shintaro Mochizuki 6-4, 6-2.
Learner Tien beat American compatriot Colton Smith 6-4, 7-5.
The Masters field is missing four of the ranking top 10, including No 1 Jannik Sinner and second-ranked Carlos Alcaraz, both due to various injuries.
The event - now controversially expanded to just under a fortnight - began two weeks after the Wimbledon final won by Sinner over Alcaraz.
Third-ranked Alexander Zverev takes the top seeding, with the German struggling recently with both his tennis and his mental health following a Wimbledon first-round loss.