Les Bleuets had lost both of their home games in the U20 Six Nations, but won on their only previous away clash in Scotland.
And here, they had a bonus point in the bag by half-time as Maxence Biasotto, Joé Quere Karaba and Zinedine Aouad, twice, all crossed.
Sialevailea Tolofua added another in the second half with Mathys Belaubre getting France’s sixth.
Wales managed a try in each half, Josh Morse and Macs Page getting on the scoreboard in a losing effort.
Both sides suffered early injuries, with France debutant hooker Mathys Lotrian and Wales skipper Harri Ackermann forced off in the first couple of minutes.
Despite playing into the strong wind, it was France who struck first. After Wales had brought down a maul illegally, France used the advantage to go to their backs, with full-back Xan Mousques bursting through before playing in Biasotto. Jean Cotarmanac’h converted from the touchline despite the conditions.
France were dominating the forward exchanges but just as it seemed they might add to their lead, Wales forced a mistake from Sialevailea Tolofua off a five-metre scrum, before earning a penalty of their own to clear their lines.
There was a clear momentum shift, underlined by France winger Nathan Bollengier earning a yellow card for an intentional knock-on. Wales took immediate advantage, Morse crashing over after a clever rolling maul. Harri Ford could not convert from out wide, but Wales were back to within two.
Just as Wales seemed to be on the front foot, France responded, Mousques putting in a beautiful 50:22 to swing field position back the way of the visitors.
They used that to put the impressive Quere Karaba over as the power of the French forward told. Cotarmanac’h converted once more.
And by half-time, they had the bonus point in the bag as Aouad crossed twice. The first followed some nice handling by the backs down the blindside, with the prop picking and going from close range to score.
Then stunning offloading and carrying from Tolofua and Quere Karaba put Aouad in again, the prop carrying two defenders over with him as he charged the final five metres. Cotarmanac’h converted and France led 28-5 at the break.
France made the stronger start in the second half, working their way into the 22 and earning a penalty – taking the decision to kick for goal as Cotarmanac’h added three more points.
Just before the hour, France brought up their fifth try in unusual circumstances. Tolofua was stood in the backline for a lineout just inside the 22. After an overthrown lineout, Thomas Souverbie was quickest to react and served Tolofua, who crashed through and carried Ford to the line before scoring. Souverbie converted to make it 38-5.
Having been under the cosh, Wales responded well. Their rolling maul was stopped initially but a sharp grubber from replacement scrum-half Rhodri Lewis was dotted down by Macs Page.
With ten minutes to go, France almost got in again as Biasotto threatened down the right, with Wales winger Harry Rees-Weldon sent to the sin-bin as he went off his feet desperately trying to win a turnover.
France took advantage of their extra man, with the powerful Belaubre crashing through the middle of the Welsh defence following a neat offload out of the back of the hand by Robin Taccola.
