Santiago, Chile ? A Socialist physician once imprisoned by Chile’s former military dictatorship held a commanding lead in the country’s presidential election on Sunday, but fell short of the majority needed to avoid a runoff with a right-wing rival.

Michelle Bachelet had 46 percent of the vote, election officials said after counting 96 percent of the ballots. Her closest rival, Sebastian Pinera, trailed with 25 percent of the vote, according to returns announced by the government.

If she wins in the runoff against Pinera on Jan. 15, Bachelet would be Chile’s first female leader and Latin America’s fourth, representing the popular center-left coalition in power since 1990. President Ricardo Lagos, who is constitutionally limited to one term, enjoys a more than 70 percent approval rating.

Bachelet invited her supporters “to work so that in January we can win.”

Pre-election polls have indicated Bachelet would defeat Pinera in a second round of voting.

The three main candidates all support the free market policies that have built one of the most prosperous economies in Latin America.

The third main candidate, the economist Joaquin Lavin, set aside the rivalry of the campaign and offered his support to Pinera as Sunday’s results became clear.