Mr Douillet had arrived on Friday, went home on Monday, and was returning again today.
He was widely regarded as one of France's best-ever athletes, the ambassador said.
"His words carry a lot of weight, not to mention the fact that he is very impressive - he is tall and very big, so when he speaks, he has natural authority. What I witnessed from the players is they really listened.
"It's good to have a leader really showing an example and personally committed to coming for that purpose."
After the minister's rallying call, France displayed their best performance in the tournament to date, beating England 19-12. "It worked and therefore we would like this to be repeated, and if the conditions are demanding the presence of a ministerial authority, as it is, he's coming back," Ambassador Etienne said.
The country was putting its hopes on a win tonight against Wales - and if Les Bleus pulled it off, Mr Douillet would stay on in New Zealand for the grand finals.
The dream was to face the All Blacks next weekend, Mr Etienne said.
"It's the last step to heaven. The team don't want to miss a step. They're completely focusing on that goal."
About 10 million people in France had tuned in to watch the quarter-finals on television, Mr Etienne said - three times as many rugby viewers as a decade ago.
Rugby was fast becoming a national sport there, he said.
But the tournament had been about more than the rugby pitch - visitors had nothing but positive things to take home, and businesses had been involved in several major networking events, Mr Etienne said.
He had been building links around New Zealand, particularly with Rugby World Cup and Foreign Affairs Minister Murray McCully, the Prime Minister, and iwi groups.
"Developing links, in my mind, means developing links with the Maori community. I think there's a huge potential in this to achieve something quite interesting in terms of shared investment."
First semifinal
France v Wales
9 tonight, Eden Park
Television schedule:
TV One: 8.30pm-11.15pm
TV 3: 8.30pm-11.15pm
Maori TV: 8pm-11.30pm
Sky Sport 1: 8.45pm-11.30pm
Rugby Channel: 8.45-11.30pm