Sylvain Marconnet rued France's failure to kill off the game as they took a half-time lead against Wales only to fall to defeat in the face of stunning attacking play from their visitors in the second period.
The Welsh completed a famous 24-18 victory at the Stade de France and the prop admitted their change of tactics in the second half, which witnessed Martyn Williams running in two tries inside five minutes, rattled Les Bleus.
Marconnet said: "We clearly wanted to go up front, pass the ball and enjoy ourselves. This is what we did in the first half.
"We had a lot of opportunities but we did not manage to convert them all. We failed to kill the match at the right time.
"The Welsh changed tactics in the second half and it unsettled us a lot. They made us weak and we ended up running after the points.
"Their two tries stunned us and we were unable to fight back. They took risks but we did not."
However the Stade Francais man insisted that it was not all doom and gloom for France and was pleased with the greater attacking threat and organisation they displayed.
He served to highlight the fact that the tournament win is still within reach and declared it is only a matter of finding the right balance before the real France show their teeth.
"We have showed a new image of the team, we proved more offensive and better organised than in our first two wins over Scotland and England," Marconnet added.
"It is a shame it ended up in a loss against Wales but once our game gets more into place both in defence and attack it will be easier.
"We have great capacities but we are still weak. The key is to find the right balance. We lost a match but not the war.
"The Grand Slam is over but a win in the tournament remains possible. We will hold on until the end. Our motivation is still huge, we are all competitors."
England Under-18 head coach John Fletcher insists his young side will be better for the experience after beating Italy in the bronze final to round out their 2015 Rugby Europe U18 Championship campaign in style.