Chris Coleman admitted Wales were still suffering from a World Cup hangover after losing 2-0 to France in a Paris friendly.
Antoine Griezmann and Olivier Giroud were on target as France underlined their World Cup credentials ahead of next summer's tournament.
France could have won by a far bigger margin, hitting the woodwork three times as Wales just about emerged with their pride intact.
But manager Coleman said Wales found their return to action after last month's World Cup elimination difficult to handle.
"We can take positives, but it was always going to be tough,'' Coleman said after the Stade de France defeat.
"Not because of their quality, but where we are mentally after losing out on the playoffs.
"There is still a bit of a hangover there and I think that will be there for a while.''
France were electric going forward with the guile of Griezmann and power of Giroud complemented by the dazzling footwork and pace of Paris St Germain teenager Kylian Mbappe.
On this evidence Didier Deschamps' side -- who were without goalkeeper Hugo Lloris and several frontline defenders through injury -- are set to be serious World Cup contenders in Russia.
"That's the best team we've ever played against, a top quality team. But we needed that,'' Coleman said.
"They scored after two good spells from us, but overall, we gave the younger players a taste of it and that's invaluable for them.''
Wales gave debuts to Chelsea teenager Ethan Ampadu and Sheffield United striker David Brooks, while Liverpool forward Ben Woodburn also came off the bench.
Coleman added: "This is the transition I've been talking about.
"We've got a few more on the bench that we need to blood. Between now and then we'll give these young boys as much experience as we can.
"International football is completely different to domestic football and unless you're on the pitch and experiencing it, you don't know what it's about.
"We're a bit subdued because we lost, but we need to take other things into consideration.''
Aaron Ramsey believes Wales' young players will benefit from facing France despite the defeat.
Ramsey said: "They're a great team with so many options so it was a tough task for us tonight.
"We took a bit of time to get going but in the end we did create a few dangerous opportunities.
"It was always going to be difficult but it's great experience as well for the younger boys coming on.
"Hopefully now we can learn from this as well and get together now and build on it for what is going to be a very important European campaign.''
France coach Deschamps was delighted with his side's performance, saying: "We had good speed and movement and we maybe could have scored more.
"The Welsh team was defending quite deep but overall it was a good game and we played quite efficiently.
"Steve Mandanda made some good saves when he had to but we had a lot of possession so we did not have to do a lot of defending.
"Maybe the substitutions disrupted our rhythm a little bit but I was pleased with the way we attacked and created chances.''