BOGOTA, Colombia – A conservative former defense minister who promises to build on Alvaro Uribe’s security gains easily defeated a maverick outsider in Colombia’s presidential election Sunday but fell short of the votes needed to avoid a runoff.

Juan Manuel Santos, a political veteran who says he’ll keep up the pressure on leftist rebels that fed President Uribe’s popularity, won 47 percent support against 21 percent for Antanas Mockus, a mathematician who ran an unorthodox clean government campaign as a Green Party candidate.

Santos, 58, needed a simple majority – 50 percent plus 1 – to avoid the June 20 runoff. He won in all but one of Colombia’s provinces and even took Bogota, considered a stronghold of Mockus, who was twice the capital’s mayor.

Uribe was barred by a February court ruling from running for a third straight term.

Finishing third Sunday with 10 percent was German Vargas of Cambio Radical, which along with Santos’ National Unity party is a member of Uribe’s governing coalition. Trailing him with 9 percent was the main opposition candidate, Gustavo Petro of the leftist Polo Democratico Alternativo.

Foreign Minister Noemi Sanin of the Uribe-allied Conservative Party won 6 percent and Liberal Party candidate Rafael Pardo, an early 1990s defense minister, got 4 percent.

Although generally peaceful, Sunday was marked by nearly two dozen clashes with leftist rebels that claimed the lives of four soldiers, a potent reminder that Colombia’s half-century-old conflict is far from resolved.

The continuing violence – and Mockus’ lack of clarity on how he would deal with it – favored Santos, a Cabinet minister in three administrations running for elected office for the first time.

Mockus committed several gaffes during the campaign that revealed his inexperience in international relations.

The outcome of the June 20 runoff “will depend largely upon the coalitions formed between the Santos and Mockus camps with the election’s ‘losers,’ ” said Arlene Tickner, a University of the Andes political scientist.

As defense minister from 2006-2009, Santos helped knock the wind out of the FARC, Latin America’s last remaining major rebel army. Authorities say it now numbers less than 9,000.

Mockus, 58, is a former National University rector who says he’ll also be tough on the FARC.