(CNN) -- Capping a hotly contested contest, Colombian President Juan Manuel Santos won re-election Sunday.
With more than 99% of polling stations reporting, he had nearly 51% of the vote versus the 45% won by challenger Oscar Ivan Zuluaga, according to election officials.
A first-round vote was held last month. None of the five candidates running then received more than 50% of votes, forcing a runoff between Santos and Zuluaga.
Santos was first elected in 2010 on a platform of continuing an offensive against the Revolutionary Armed Forces of Colombia, or FARC, leftist guerrillas at war with the government for decades.
But since late 2012, peace talks with the group have become a hallmark of the Santos presidency.
Zuluaga had called for an end to the peace talks and is against giving any political space to the rebels.
He conceded Sunday night, thanking supporters and promising to continue to fight for the good of the nation.
Santos celebrated in Bogota, predicting the start of a new Colombia.
"These have been unique elections (because) what was at play wasn't the name of a candidate -- but the direction of the nation. Colombians with very different ideas ... came together around a cause," he told cheering crowds, "and that cause is peace."
"This is the end of more than 50 years of violence in this country, and the beginning of a new Colombia," Santos said.
CNN's Catherine E. Shoichet and Rafael Romo contributed to this report.