Alcaraz dumped out of Paris Masters by 18th-ranked Humbert in third round
Left-handed Humbert came through 6-1, 3-6, 7-5 to register his first win over the French Open and Wimbledon champion having lost twice to the Spanish star earlier in 2024.
It was a testing evening for Alcaraz who was 0-5 down in the first set before he managed to get on the board.
"I'm just super proud of myself that I did it," said Humbert who has won titles in Marseille and Dubai this season.
"It was a crazy match, a crazy atmosphere."
"I went for every shot," added Humbert, looking back on his first set blitz.
"That's why I think I had less energy in the second set and after in the third it was a mountain that was with me from the beginning of the third set to the end.
"I trusted myself in big moments and I made some big shots."
Alcaraz has endured a rollercoaster second half of the season since his heartbreaking Paris Olympics final loss to Novak Djokovic.
He was knocked out in the second round of the US Open by 74th-ranked Botic van de Zandschulp, defeated top-ranked Jannik Sinner in the Beijing final before a quarter-final exit at the hands of Tomas Machac, the world number 33, at the Shanghai Masters.
Humbert goes on to face Australia's Jordan Thompson for a place in the Paris Masters semi-finals.
The French number one just edged Alcaraz in winners on Thursday with 28 to 23 with both men committing 38 unforced errors.
Thompson, ranked at 28, made the quarter-finals of a Masters event for the first time by beating Adrian Mannarino of France 7-5, 7-6.
Meanwhile, Alex de Minaur's bid to become the first Australian to make the ATP Tour Finals since Lleyton Hewitt 20 years ago, were boosted when the ninth seed defeated in-form Jack Draper of Britain 5-7, 6-2, 6-3.
The win moved De Minaur into the eighth and final qualifying spot for the Turin end-of-season showpiece.
"I'm going to put my body on the line, try my hardest, show my opponent that I can do that all day.
"I needed to bring that intensity because Jack is a hell of a competitor, playing with so much confidence right now," said De Minaur.
He next faces 13th-seeded Holger Rune of Denmark who ended the run of French lucky loser Arthur Cazaux 3-6, 6-3, 6-4.
