And Mermoz admits France tried to sit on their lead rather than attack the Welsh, a mistake they cannot afford to repeat against the All Blacks.
Mermoz said: "We won't be able to take that sort of pressure for a whole game against a team like New Zealand.
"We've won a European competition in beating England and Wales, it was a bit like the Six Nations.
"Now it's a level above and we'll have to come up with a mix of the quarter and the semi to produce a big match.
"We were all scared against the Welsh. It didn't feel like they were down to 14. The problems come from what we did, and what we should have done.
"We turned over three balls at the start, we should have kicked but we counterattacked poorly and conceded three penalties.
"I think that really blocked us even though we went out there wanting to play.
"As soon as we took the lead, as often happens, we waited for the time to pass.
"It's what we did against England, we stopped playing in the second half. There it was the same again."
But while few give France a hope of winning the repeat of the 1987 final, Mermoz believes Les Bleus' biggest problem remains a mental issue when it comes to the Southern Hemisphere big three.
He added: "I think it's a mental problem. Now and again we manage to react and raise our level but then we suffer again.
"We've been very passive, and that comes from the head. We were very tense. We watched the game go by, we want to lift our heads and take control of the final."