SANTIAGO, Chile — Former president Sebastián Piñera of Chile, a conservative billionaire, on Sunday won the first round of an election to choose a successor to President Michelle Bachelet.

Piñera, 67, who won 36 percent of the vote, will compete in a runoff election Dec. 17 against a center-left journalist and former news anchor, Alejandro Guillier, 64, who received 22 percent of the ballots cast.

The election was the first under new electoral rules in Chile that limit campaign spending and impose greater transparency on it. The rule changes also made voting voluntary and granted Chileans living abroad the right to vote, though only 11 percent of those eligible to vote in 62 countries registered to do so.

Voter turnout overall was low — about 45 percent of those who could cast ballots did so — in keeping with a fall in electoral participation since the return to democracy in Chile in 1990 after 17 years of military dictatorship.

A group of demonstrators forced their way into Piñera’s campaign center to protest the elections. More than 20 were arrested.

New York Times