Argentina gatecrashed France's World Cup party on Friday when they kicked off the six-week marathon with a stunning 17-12 upset over the hosts in front of 80,000 people in the Stade de France.
The result delivered a major dent to France's hopes of qualifying for the quarter-finals from a Pool D which also includes Six Nations Triple Crown winners Ireland.
It was also a blow for the country's sporting prestige which was so badly bruised by the loss of the 2012 Olympics to London.
"We are overcome with happiness, but we shouldn't get above ourselves because it is only the first match," Argentina coach Marcelo Loffreda said.
The Pumas scored all of their points in the first half with Ignacio Corleto scoring a breakaway try and Felipe Contepomi, playing alongside brother Manuel, kicking the other points.
David Skrela kicked France's meagre four-penalty response.
"When you begin a World Cup, and it is imperative to win the match and you lose, you can say only one thing that the sky has fallen in on your head," France coach Bernard Laporte said.
The defeat was a shattering let down for France which has invested millions in the tournament and has seen the 10 venues in the country bedecked in the French tricolor and submerged in World Cup hype.
Even the Eiffel Tower has been drafted in on the act with a giant, illuminated rugby ball draped beneath the famous structure.
Before Argentina's heroics, the Stade de France enjoyed a colorful opening ceremony.
There was a parade of the 20 greatest all-time players, like Jonah Lomu and French legend Jean Pierre Rives, while the festivities featured 200 dancers and music under the guidance of leading choreographer Olivier Massart.
In the center of Paris, meanwhile, 4,000 people gathered to watch the ceremony as well as the match on a giant screen erected outside the Hotel de Ville.
International Rugby Board chairman Syd Millar welcomed the fans and teams.
"The International Rugby Board welcomes you all to this marvellous festival of world rugby," he said.
"Each rugby World Cup has been better than the last, and this will prove no exception. Rugby is rightly proud of its ability to retain high standards of sportsmanship, ethical behavior and fair play," he said.