Chile’s former President Michelle Bachelet and ruling alliance candidate Evelyn Matthei said they will face each other in a presidential runoff scheduled for Dec. 15.

Bachelet, 62, won 46.8 percent of the votes in the race to succeed President Sebastian Pinera, the electoral service said on its website after 90 percent of the ballot boxes were counted. Matthei had 25.1 percent. A candidate needs more than 50 percent of the votes to win in the first round.

Bachelet is promising $15.1 billion in extra spending over four years in response to protests over the quality of schooling and hospitals that helped drive President Sebastian Pinera’s approval rating to a record low. Matthei says her rival’s plan will jeopardize thirty years of almost uninterrupted growth that has made Chile the wealthiest country in Latin America.

“Today the Chileans voted for a tax reform that will allow for better education and health care,” Bachelet said. “We are going to have a decisive and convincing victory in December.”

Matthei, who said on Oct. 30 that Bachelet’s proposal were a throwback to the era of the Berlin Wall, said she represented the continuity of “a successful economic model.” Under Pinera, Latin America’s richest economy saw unemployment fall to the lowest in at least 30 years.

The opposition believes “in tearing everything down and starting from zero with a new constitution,” Matthei told supporters after preliminary results were released.

Both Matthei and Bachelet are daughters of air force officials. While Matthei’s father rose through the ranks after the 1973 coup that brought Augusto Pinochet to power to help lead the military junta, Bachelet’s father was imprisoned and tortured to death by the regime, according to a report by the state forensic medical service.

Voters also chose all of Chile’s 120 deputies in the lower house of parliament today and 20 of 38 senators. Bachelet’s alliance currently has 57 deputies and 20 senators.

Bachelet will need a majority in both chambers to ensure the success of her tax overhaul, including the increase in the corporate tax rate to 25 percent from 20 percent and the end of a 30-year incentive to reinvest profits.

The changes will bring Chile more into line with its counterparts in Latin American, where Colombia has a corporate tax rate of 25 percent, and Peru and Mexico have 30 percent. Five years ago, Chile had a tax rate of 17 percent, half Colombia’s 33 percent.

“When I read Michelle Bachelet’s program, there are things that don’t point in the right direction and that threaten development, growth, and small and medium enterprises,” Pinera said in an interview with Radio Duna on Nov. 12. “This election is very important.”

Pinochet’s tax changes in 1984 cut the corporate tax rate to as low as zero. The system helped double the investment rate to 24.5 percent of GDP in 1988 from 11.9 percent in 1983, according to the International Monetary Fund.

Since 1983, Chile has averaged economic growth of 5.2 percent a year, raising income per capita to about $19,100, the highest in South America, according to the IMF.

Bachelet, who ran Chile from March 2006 to March 2010, denies she will put Chile’s economic success in jeopardy. During her presidency, dollar-denominated bonds returned 32 percent, three times more than under the current administration and more than the 27 percent gain on similar Latin American bonds during her tenure, according to Bank of America Corp.

Chile has the most socially segregated schooling system in the OECD, with few of the poor entering the top performing schools, according to research released by the organization on Sept. 13, 2011. More than 85 percent of higher education is financed by students and their families, the OECD said.

Pinera’s approval rating fell to a low of 26 percent in April of 2012, a year after the student protests started and down from a high of 63 percent toward the start of his government, according to monthly polls by GFK Adimark. The rating climbed to 40 percent last month.

The winner of Chile’s election may face slower growth in their first year in office. Policy makers reduced their growth forecast for this year on Sept. 4 to between 4 percent and 4.5 percent from 4 percent to 5 percent, citing weaker external conditions and a slowdown in the first half of the year.

A drop in copper prices and higher global borrowing costs could lead the economy to grow less than 4 percent in 2014, according to former central bank presidents Vittorio Corbo and Jose De Gregorio.

To contact the reporter on this story: Javiera Quiroga in Santiago at jquiroga5@bloomberg.net