(Reuters) – Former Colombian Defense Minister Juan Manuel Santos took a big lead in the first round of a presidential election, but looked headed for a June runoff against rival Antanas Mockus, initial results said on Sunday.

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Santos, an ally of President Alvaro Uribe, led with 46.8 percent of votes, while Mockus, a former Bogota mayor, had 21.38 percent with about 52 percent of polling stations counted, according to electoral authorities.

Neither candidate appeared likely to win the more than 50 percent votes to clinch outright victory.

A staunch Washington ally, Uribe steps down in August still popular after two terms dominated by his war against drug-trafficking rebels, and his pro-business approach that attracted foreign investment especially in oil and mining.

Santos, a U.S.- and British-educated economist, led early campaigning, but Mockus, the son of Lithuanian immigrants who is also a former university professor, surged with a Green Party campaign against graft and “politics as usual.”

Both front-runners say they will keep Uribe’s tough security and pro-market economic policies applauded by investors, and analysts see little long-term impact on the peso or local TES bonds whoever wins.

Polls show Colombians now more concerned with joblessness, education and healthcare than guerrilla violence, and many become weary of the scandals over human rights and corruption that blemished Uribe’s second term.

Alliances will be key in a second round. As head of Uribe’s U Party, Santos will seek out the Conservative and Cambio Radical parties. Mockus, whose Green Party, has few seats in Congress, claims the moderate middle ground.

The next leader inherits better security and investment but also a slow economic recovery, a wide deficit, double-digit unemployment and a trade dispute with Venezuela, where socialist President Hugo Chavez is riled over U.S. influence.

(Reporting by Bogota newsroom; Editing by Peter Cooney)