(Adds latest vote count, comment from Pinera's campaign chief)
By Felipe Iturrieta and Dave Sherwood
SANTIAGO, Nov 19 (Reuters) - Chileans voted for a successor to President Michelle Bachelet on Sunday, with billionaire conservative Sebastian Pinera leading in preliminary results, though he will almost certainly face a December runoff against a left-of-center candidate.
With around 70 percent of votes counted, Pinera, who was president between 2010 and 2014 and leads the Chile Vamos bloc, had won 37 percent of support, electoral agency Servel said.
Pinera needs 50 percent for an outright win.
The early results showed weaker-than-expected support for Pinera, whom pollster CEP forecast receiving 42 percent of votes late last month.
"We have a lead which is good, and we're going to have a very competitive second round," Pinera's campaign chief Andres Chadwick told journalists as the results came in.
Former TV anchorman, Senator Alejandro Guillier, the flagbearer for Bachelet's fractured center-left Nueva Mayoria coalition, was coming in second with 23 percent.
Leftist Beatriz Sanchez was snapping at his heels with 20 percent, closer than opinions polls had suggested.
The election is the latest in South America to pit left-leaning politicians against the conservatives increasingly taking their places.
Pinera has pitched himself as a vote for a brighter future, tapping into widespread discontent with Bachelet's government, which coincided with an economic downturn in the top copper exporter.
"Today we're going to make a decision that will impact our lives for many decades," Pinera told journalists after voting at a school in Santiago on Sunday. "I know we're going to pick the right path, the one that takes us to better times."
The vote is a turning point for Chile's coalition of center-left parties, previously known as the Concertacion. The pact, which for decades has dominated Chilean politics, fissured under Bachelet, riven by disagreements over policies such as loosening Chile's strict abortion laws and strengthening unions.
Bachelet, who is barred from running in this election by term limits, will step down with approval ratings near 30 percent and the legacy of her social and economic policies uncertain.
Many Chileans view the election as a referendum on her second term, which focused on reducing inequality by expanding access to free education and overhauling the tax code.
Pinera, the market favorite, has campaigned on a platform of scaling back and "perfecting" her tax and labor laws, seen by many in the business community as having crimped investment at a time when slumping copper prices were already driving down economic growth.
"Pinera's the best candidate. Plus, he already governed. We know who he is," said Fresia Jara, a 73-year-old retiree as she left a polling station in the capital Santiago.
Pinera garnered international attention and domestic praise for his handling of the dramatic rescue of 33 trapped miners during his prior term in 2010, and is seen as a safe pair of hands by investors.
But his administration was marred by massive student protests seeking an education overhaul. His responses were often seen as out of touch and grassroots groups still oppose him.
Guillier, who is ideologically aligned with Bachelet, has promised to deepen her reforms and has tapped support from Chileans who view Pinera as a setback for gains made for students, women and workers.
"I voted for Guillier because I think we have to continue to provide free education. It's a social right," said unemployed voter Mario Giannetti, 53.
Sanchez had criticized Guillier on the campaign as too similar to Pinera, and proposed a deeper departure from the country's business-friendly policies, including much higher taxes on mining companies.
Sanchez, who represents the leftist Frente Amplio party, sought to tap the energy of student and protest groups who seek better health and education and are frustrated with Chile's longstanding free-market model.
Juan Pablo Maldonado, a 30-year old electrical engineer from Santiago, said he'd planned to vote for Sanchez because her coalition represented a break from business as usual.
(Reporting by Dave Sherwood, Felipe Iturrieta and Antonio de la Jara, writing by Mitra Taj; editing by Rosalba O'Brien and Grant McCool)
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