By Michel Rose
PARIS (Reuters) - Emmanuel Macron's camp should perhaps keep the champagne on ice a little longer.
The young independent centrist's qualification on Sunday for the runoff of France's presidential election in two weeks' time will certainly bring a sigh of relief in European capitals and financial markets; opinion polls suggest he will beat his far-right rival Marine Le Pen with ease.
But to have a real chance of implementing the reform of France's economy and politics that he wants, he needs a victory big enough to enlist popular figures from established parties in the parliamentary election that follows in June.
According to an almost-complete count, Macron beat Le Pen by around 24 percent to 22 percent.
It may have been a huge triumph for a 39-year-old never elected to public office who was virtually unknown in France before becoming economy minister three years ago, and only founded his political movement last year.
But it was also, in a packed field, the lowest score of any first-round winner since 2002.
Then, it was Jacques Chirac who scored only 20 percent - but benefited from a joint effort by all mainstream parties to block his National Front challenger, Le Pen's father Jean-Marie, to secure a crushing win in the runoff by 82 percent to 18.
This time, the mainstream conservatives and Socialists also quickly urged their supporters to vote to block Marine Le Pen.
"He's going to adopt a rallying posture just like (former president Jacques) Chirac did in 2002," said Francois Kraus of pollsters Ifop.
But in 2017, the endorsements of conservatives and Socialists combined accounted for only 26 percent of votes.
Analysts say that if Macron fails to win more than 60 percent in the second round, he may find it hard to reassure a divided country that he has what it takes to reform the euro zone's second-largest economy, which is only starting to pick up speed after five years of anemic growth.
Then, in turn, he might struggle to turn his promise to transcend traditional party divides into a working majority for his En Marche! (Onwards!) movement in June's parliamentary election, six weeks later.
Macron addressed that head-on in his victory speech, saying that "the power of the momentum behind me will be the key to my ability to lead and govern".
Two surveys conducted on Sunday put him on 64 and 62 percent respectively for the second round.
But in Le Pen, the former Rothschild investment banker faces a formidable rival.
"It's more complicated than it looks - a new campaign is starting," said Francois Miquet-Marty of pollster Viavoice.
"Marine Le Pen is going to frame this as a face-off between Emmanuel Macron, the candidate of the globalized elite, and herself as the people's candidate," he said. "She has a line of attack that can hit the bullseye."
And endorsements from mainstream parties could also work against Macron in a country where the divide between 'haves' and 'have nots' has been pushing up support year after year for Le Pen's message that only she can defend French workers' jobs and rights.
On Sunday night, Le Pen and her allies dismissed Macron as the candidate of a dying establishment: "Change is obviously not going to come from the heir of (outgoing president) Francois Hollande and his disastrous mandate of failures," she told supporters.
Miquet-Marty said Macron would "need a more offensive approach, and to distill the message that a Macron presidency would be more peaceful than a Le Pen one".
Again, Macron hinted at this when he told supporters: "The challenge from tonight is not to go and vote against whoever it might be; the challenge is to decide to break completely with a system that has been incapable of dealing with our country's problems for more than 30 years."
In his favor, analysts say, is the fact that 35 percent of voters thought Macron was the best candidate to put the French economy on the right track, against only 20 percent for Le Pen, according to a recent Odoxa poll.
Meanwhile Le Pen's anti-euro stance, which is rejected by many of her own supporters, as well as a majority of voters, offers him a promising line of attack.
Many analysts are now turning their attention beyond his expected victory in the second round to ask whether he can gather the political muscle to enact his program.
Macron says his party will field candidates in all 577 constituencies, but he has also made clear that he will welcome those from other parties who share his views.
Some 50 Socialist legislators have already signed up to his movement, including some heavyweights, but the bigger his second-round score, the more attractive it will be for others to follow suit. He might have to make do with a coalition government.
To many analysts and investors, the question is whether Macron's government, of whatever shape, can push through policies -- such as relaxing some labor laws -- that are likely to run into public resistance and have defeated previous, seemingly stronger admistrations.
"His parliamentary majority could be extremely fragmented. We could find ourselves in a situation similar to what happened under the Fourth Republic, with an unstable majority," said political analysts Philippe Cossalter of Sarre University.
Raphael Brun-Aguerre of JPMorgan Chase Bank said it would be very difficult for Macron to secure a majority in the lower house, adding: "We thus expect him to try to form a cross-party coalition around a narrow set of reforms."
Macron's answer is that he has spent the last year proving the pundits wrong, and will do so again.
"They're taking the French for idiots," he said at a recent rally. "The French are consistent. That's why, six weeks later, they will give us a majority to govern and legislate."
(Additional reporting by Leigh Thomas; Ingrid Melander, Mathieu Rosemain and Emmanuel Jarry; Editing by Andrew Callus and Kevin Liffey)