A Jekyll and Hyde display from Les Bleus saw them take a 17-point lead in the first half as Gael Fickou and Antoine Dupont crossed within four minutes of each other at the end of impressive moves.
But the Pumas roared back and were soon leading after using their set-piece to get Guido Petti Pagadizabal and Julian Montoya over from lineouts.
Lopez's first act after coming on as a replacement was to kick the winning points, with Emiliano Boffelli missing a last-minute penalty and the final whistle was followed by a short brawl between the two sets of players.
Nicolas Sanchez slotted through a penalty after a bulldozing run by Petti Pagadizabal but France moved ahead when Virimi Vakatawa dropped Pablo Matera and fed Fickou, who stepped in off the left and stretched over in the 17th minute.
A surge down the right from Damian Penaud proved key to Les Bleus' opener and, after some terrific hands in the build-up, the wing offloaded in the tackle for Dupont to go over in the corner.
After adding the extras to both tries, Romain Ntamack contributed a pair of three-pointers either side of some stoic try-line defence to send France into the break 20-3 up.
The Pumas meant business after the restart and had their first try within two minutes, Petti Pagadizabal making the most of the decision to opt for a lineout rather than a kick at goal from a penalty.
Argentina repeated the trick in the 53rd minute and Montoya touched down off the rolling maul, but Sanchez, having appeared to hurt his shoulder in the first half, missed the conversion and was replaced by Benjamin Urdapilleta, who quickly reduced the deficit to two points.
Urdapilleta edged the Pumas ahead for the first time after the television match official (TMO) decided Boffelli's aerial challenge with Penaud, which saw the wing leave for a head injury assessment, was fair.
Lopez's ambitious drop goal just about had enough length on it and Fickou was let off the hook by Boffelli after a clumsy tackle on the full-back, whose 53-metre penalty curled narrowly wide to give France the win.
In a pool that also includes England, it always seemed likely that the winner of this game will follow it into the quarter-finals. Having fallen in their opener, Argentina will need a big performance against Eddie Jones' side if it is to revive hopes of progression.
Argentina takes on Tonga in Higashiosaka next Saturday, while France is not in action until its match with United States in Fukuoka on 2 October.