Gianni Alemanno took 53.6% of the vote to 46.3 percent for Francesco Rutelli, a former two-time center-left Rome mayor, according to the municipality.
The conservative candidate entered the race as the underdog, but successfully rode the momentum of Berlusconi's triumph in national elections two weeks ago to win the runoff against Rutelli that took place Sunday and Monday.
Since the end of WWII, the Italian capital has been governed mainly by Christian Democrat or leftist administrations.
Hundreds of Alemanno supporters celebrated in Michelangelo's Piazza del Campidoglio, in front of the municipal offices, waving Italian flags and singing the national anthem.
Speaking earlier at his headquarters, Alemanno promised to be a mayor for all Romans.
"This wasn't a victory for a party but for the whole of Rome," he said. "The result shows I received broad support and I will take that into account when governing the city."
Alemanno focused his campaign on demands for improved security, in the wake of a crime wave blamed mainly on foreigners. He pushed for a change after 15 years of center-left administrations led by Rutelli and later by Walter Veltroni, who quit the post earlier this year to challenge Berlusconi in the national vote.
Alemanno, a former agriculture minister in one of Berlusconi's governments, is a leader of the National Alliance — a former neo-fascist party that turned mainstream conservative and is a key Berlusconi ally.
In the first round two weeks ago, Rutelli won 45% of the vote, against 40% for the conservatives. But Alemanno may have jumped ahead thanks to the votes of small centrist and far-right parties whose candidates were eliminated.
(Roma, 28 aprile 2008)