UPDATE 3-Chile's Pinera takes commanding lead in presidential vote

(New throughout, updates count)

SANTIAGO, Dec 17 (Reuters) - Conservative challenger Sebastian Pinera was on track to win Chile's presidential election on Sunday, after pledging to end his center-left predecessor's progressive agenda and jump-start growth in one of Latin America's most developed economies.

With 82.2 percent of the vote counted, Pinera, 68, had won 54.5 percent in the run-off election, to 45.5 percent for the center-left Alejandro Guillier, a wider than expected margin in a race that pollsters had predicted would be tight.

The campaign exposed deepening rifts among the country's once bedrock center-left, an opening former president Pinera leveraged to rally more centrist voters around his proposals to cut corporate taxes, double economic growth and eliminate poverty in the world's top copper producer.

Pinera's supporters cheered at campaign headquarters as the results were swiftly tabulated on a sunny Santiago evening.

Many Chileans viewed the election as a referendum on outgoing President Michelle Bachelet's second term, which focused on reducing inequality by making education more affordable and overhauling the tax code.

Though neither candidate would have marked a dramatic shift from Chile's long-standing free-market economic model, a Pinera victory underscores an increasing tilt to the right in South America following the rise of conservative leaders in Peru, Argentina and Brazil.

Pinera painted Guillier, a former TV anchorman and current senator, as extreme in a country known for its moderation, and likened him to Venezuela socialist President Nicolas Maduro.

But Pinera's own conservative agenda may also struggle, at a time when efforts by his ideological allies in Brazil and Argentina to reduce fiscal deficits by cutting spending have faced political opposition and sparked protests.

The investor favorite, Pinera's proposals are seen as miner-friendly in a country where copper is king. He has pledged support and stable funding for Chile's state-run miner Codelco , and has promised to slash red tape which had bogged down projects under Bachelet.

After a leftist party made unexpected gains in November's first round, Pinera sought to woo less well-off voters with proposals such as the creation of a public pension fund to compete with Chile's much-criticized private pension funds, and the expansion of free education.

The race marks a turning point for Chile's historic coalition of center-left parties, previously known as the Concertacion. The pact fissured under Bachelet, riven by disagreements over policies such as loosening Chile's strict abortion laws and strengthening unions.

Pinera seized on the backlash, campaigning on a platform of scaling back and "perfecting" her tax and labor laws, seen by many in the business community as crimping investment at a time slumping copper prices were weighing on the economy.

"I voted for Pinera because I am an entrepreneur. I value my own efforts and do not expect much from the government," said Rosario Poma, 53. "I think (Pinera) will be good for investment."

(Additional reporting by Felipe Iturrieta and Caroline Stauffer; Writing by Caroline Stauffer; Editing by Jeffrey Benkoe and Rosalba O'Brien)