Jean-Francois Cope, a Sarkozy ally who reached out to the far right by leading a legislative effort that banned face-covering Muslim veils, defeated moderate former Prime Minister Francois Fillon in the Sunday vote.
Each candidate initially claimed victory Sunday night in the tight race, and each claimed pockets of vote rigging. It took 24 hours more before the final result was announced by the electoral commission of the UMP, as the party is known: 87,388 to 87,290.
Cope, a former budget minister who has led the Union for a Popular Movement since Sarkozy bowed out to become president in 2007, will lead opposition to President Francois Hollande's Socialists, who control both houses of parliament and nearly all of France's regions.
In the spring, after a decade in power, Sarkozy's conservative party lost both the presidency and control of the National Assembly to the Socialists.
The long-united party, still licking its wounds from the electoral defeats in the spring, was a shadow of itself by Monday night. There was so much disarray and anger within the ranks that former Prime Minister Alain Juppe warned that "there is a real risk of a rupture."
Cope called on party members to get over the division and get to work.
"It's now time for the electoral period to end, and time for work to begin, starting tomorrow morning," Cope said.
Fillon denounced the "moral and political fracture" within the party. However, he indicated he would not contest the results.
Laurent Wauquiez, a former European affairs minister, said the dispute gave the party a "very bad image" and former Agriculture Minister Bruno Le Maire called the situation surreal. In a blog entry entitled "Stop!" Juppe, wrote: "We have to get out of this lamentable situation to avoid the explosion of our party."
On Monday night, Cope confirmed the party's tack toward right, saying that the "right without complexes" is back.
Many saw the Cope-Fillon showdown as jockeying for position to lead the party up to the next presidential and legislative elections in France in 2017.
France doesn't have any elections again until 2014—when voters will elect mayors, regional officials and European Parliament lawmakers. Cope set his sights on a massive win by conservatives in 2014, calling that the party's "first mission."
Party leadership is seen as a possible springboard to the presidency, allowing a politician to glad-hand among the rank-and-file and build up the party machine in his or her image. Sarkozy and Hollande are among many French postwar party leaders who eventually won the presidency.
Elaine Ganley contributed to this report.