Despite a spirited comeback from the U20s during the second half of the match, France took away a win of 19-10.
In glorious conditions, France took the lead inside seven minutes when a Dafydd Howells kick was charged down, for Arthur Bonneval to cross for his side's opening try.
Six minutes later it was 12-0. This time Thomas Ramos nipped in at the corner for a try the full back duly converted.
To their credit, Wales established themselves thereafter with Allan Lewis' pack more than holding their own at scrum and line out. Sadly, they were careless with ball in hand and chances came and went.
The worst of these came 10 minutes from half time when Howells, with the line at his mercy, knocked on over the line. Hooker Ryan Elias and scrum half Tom Williams were amongst those who had try scoring opportunities during the game but couldn't quite finish them off. Outside half Dan Jones kicked Wales' only points of the first half through a penalty.
If the first half had been somewhat disappointing, the second was hugely frustrating. Wales had plenty of ball, but knocked on with alarming regularity.
From one such error, France broke from their own 22 through Ramos and centre Damian Penaud. The latter flicked a neat inside pass to Lucas Blanc who galloped over. Ramos converted but kept Wales in the game with a series of missed penalties.
With 19 minutes remaining, a line-out deep in the French 22 provided a platform from which a try finally came.
The Welsh forwards showed patience in driving to the line and when the ball came out to Garyn Smith, the Pontypridd and Blues centre muscled his way over for his club and regional team mate Jarrod Evans to convert.
A flurry of opportunities ensued, but once again, careless handling and wrong options cost Wales the chance of at least closing the gap further. In the end, France held on and kicked off the race to win Pool A with a valuable victory.
Wales Under 20 v France Under 20 Squad:
Dafydd Howells (Ospreys); Lloyd Lewis (Dragons), Owen Watkin (Ospreys), Garyn Smith (Blues), Joshua Adams (Scarlets), Dan Jones (Scarlets), Tom Williams (Blues); Luke Garrett (Dragons), Ryan Elias (Scarlets), Dillon Lewis (Blues), Adam Beard (Ospreys), Rory Thornton (Ospreys, captain), Tom Phillips (Scarlets), Ollie Griffiths (Dragons), Harri Keddie (Dragons).
Replacements: Liam Belcher (Blues), Keagan Bale (Dragons), Leon Brown (Dragons), Seb Davies (Blues), Jon Fox (Ospreys), Kieran Hardy (Scarlets), Jarrod Evans (Blues), Barney Nightingale (Dragons).
Referee: Matthew Carley (England)
