Coach Bernard Laporte insists France can bounce back from their shock World Cup loss to Argentina but admits they buckled under the enormous expectation.
France's Damien Traille finds defeat to Argentina hard to take
"We won't let our heads drop - France will still play a key role in this World Cup," said Laporte.
"We were fragile and couldn't cope with the pressure. Players were jittery."
To increase French misery, fly-half David Skrela was ruled out of the 21 September clash with Ireland because of a left Achilles tendon injury.
If Les Bleus are to be crowned world champions for the first time, they will need to make tournament history.
No team has ever won the competition after losing the opening match, but that is the challenge now awaiting Laporte's players.
Pumas full-back Ignacio Corleto, who plays his club rugby in Paris with Stade Francais, scored an interception try that helped Argentina establish a 17-6 lead.
Four Felipe Contepomi penalties also played their part in keeping France at bay, and a shocked Laporte struggled to comprehend the enormity of his team's Pool D loss.
"At least we got a losing bonus point," he said.
The expectation on us for this first game was enormous, and we weren't tough enough to deal with that
France skipper Raphael Ibanez
"We were counting on this match to get the World Cup campaign momentum going and we failed. We were fragile and febrile.
"We did not know how to lighten the pressure on the players and certain of them did not play to their best.
"However, I am convinced that this group has something about them and they will react to this.
"I believe in this squad, in these players. It is vital to raise our heads, immediately."
France were favourites to top the pool and face a probable home quarter-final against either Scotland or Italy.
But their defeat leaves them battling to avoid elimination.
They must now effectively beat Ireland in Paris in two weeks' time to reach the last eight.
Even a win might only be good enough to secure them second place in the group - and a likely clash with tournament favourites New Zealand in Cardiff.
"It's a big, big disappointment for the whole team," said skipper Raphael Ibanez.
"But we still have three games to go in this group, and we will have to work even harder.
"The expectation on us for this first game was enormous, and we weren't tough enough to deal with that."
Centre Yannick Jauzion added: "We have to give everything now to get this first place, even if we are not masters of our destiny.
"Everyone is devastated but we have to stick together but we didn't know how to raise our heads when we were down."