Morale-boosting Metz win for Andy Murray
The Scot looked set to pay the price for failing to convert a series of break point chances before he found his range to dispatch the world number 26 4-6 6-3 6-2.
Murray had pushed world number three Stefano Tsitsipas to five sets in the first round of the US Open last month, before a low-key defeat in a Challenger in Rennes last week.
And the manner of his display against the accomplished Humbert ought to give him plenty of encouragement that he can finish another difficult season on a high.
Murray, a finalist in Metz in 2007, fell a set behind when Humbert seized his first opportunity with a flashing stop-volley to break for a 5-4 advantage, then served out for the set.
Murray dug himself out of a hole at 3-3 in the second set, before seizing on an increasing number of errant forehands from his opponent to take his ninth break point opportunity and, like Humbert, duly serve out for the set.
Seemingly shrugging off any lingering fitness concerns, Murray roared into a double-break advantage at the start of the decider to silence the fans who had cheered Humbert to his early advantage.
Saving two break points at 4-1, then another two games later with a brilliant backhand pass, Murray ultimately served out to set up a second round clash with Vasek Pospisil