There was no less tension in the final set, which also went to a tie-break.
Mustering whatever strength he had left after almost three hours of play, Humbert did the unthinkable and polished off the 2021 US Open champion 7-2 in the tie-break to send shockwaves through the tennis community.
It was the biggest win of the Frenchman's professional career to date.
North American showdown
Two traditional rivals went head-to-head at the ATP Cup on Sunday but a hilarious moment before the second of Canada's clashes with the USA certainly helped break the tension.
Just hours before play began, Canadian left-hander Denis Shapovalov withdrew from his team's first singles match of the day, citing fatigue following his time in isolation with Covid-19.
The World No. 14 tested positive on arrival in Sydney and while he has since been released from biosecurity protocols, opted to sit the match out.
"I'm disappointed not to be able to play the first match, but I just didn't feel ready physically yet, so we did what is best for the team," he said.
The 11th hour withdrawal pushed World No. 238 Brayden Schnur into the limelight, where American World No. 24 John Isner took just over an hour to steamroll him in straight sets.
The second clash, contested by World No. 11 Canadian Felix Auger-Aliassime and America's Taylor Fritz (No. 23) got off to an inauspicious start.
As is customary, the pair posed either side of the net for a picture before the match.
However, no photographer turned up to capture the top-seeded players from the rival nations, leaving the players smiling into the abyss.
"There's no photographer, you can leave," said a match official, realising the error.
The players then dispersed for what began as a tightly-fought contest.
Fritz ultimately defeated his opponent to ensure the USA would clinch victory over Canada with a match in hand.
