The Harvard-educated Pinera had 44 percent to 30 percent for the ruling center-left coalition's candidate, former President Eduardo Frei. Breakaway Socialist Rep. Marco Enriquez-Ominami had 20 percent, and communist Jorge Arrate had 6 percent, with 98 percent of the votes counted.
The key question in the Jan. 17 runoff between Pinera and Frei is whether leftists can unify to fend off the most moderate candidate Chile's right has ever had.
A win by Pinera, 60, would install a right-wing government in Chile for the first time since Gen. Augusto Pinochet's 1973-1990 dictatorship but only if Pinera persuades enough leftists to take a chance on him.
"We have to understand that this win doesn't belong to us," Pinera said in a victory speech to his party members. "It belongs to all Chileans, to the humble people, to the poor and the middle class, the people who most need change from their government."
Frei appealed for leftists to come together, saying he would take on his rivals' ideas as if they were his own, that women and young people would have a prominent place in his government, and that he would push for reforms to end the big alliances' domination of the political process.
"The people have told us that there are things they don't like, that things must change, and I share this mission," said Frei, 67.
But even though he may be encouraging a right-wing victory, Enriquez-Ominami refused to endorse Frei in his concession speech, instead inviting his followers to vote their consciences.
"Eduardo Frei and Sebastian Pinera are too much alike," he complained. "They don't represent hope, nor change, nor the future."
Stability and experience are selling points for Frei, who governed from 1994 to 2000.
"We don't want leaps into the unknown, nor do we want to return to the past. We want a government that worries about the people," he said after voting. "We don't believe that the power of the market and money should have priority over a society."
But many voters are fed up with having the same government throughout 19 years of democracy following Pinochet. Promising change, Pinera and Enriquez-Ominami challenged the ruling coalition like never before.
Outgoing President Michelle Bachelet has 78 percent approval ratings and Chile seems on track to become a first-world nation.
Chile's economy, negligible inflation and stable democracy are the envy of Latin America. Booming copper revenues and prudent fiscal policies have helped the government reduce poverty from 45 percent in 1990 to 13 percent today, raising per capita annual income to $14,000 in the nation of 17 million.
But a huge wealth gap between rich and poor and a chronically underfunded education system have many voters feeling more must be done to redistribute Chile's copper wealth. A study by the World Bank several years ago showed that the poorest 10 percent of Chileans benefit from only 1.3 percent of government revenues, while the richest 10 percent benefit from 40 percent.
Pinera ranked No. 701 with $1 billion on the Forbes magazine world's richest list. He built his fortune bringing credit cards to Chile, and his investments include Chile's main airline, most popular football team and a leading TV channel.
Whether Pinera can apply the same entrepreneurial spirit to the presidency will depend on voters who backed Rep. Enriquez-Ominami, a renegade Socialist and documentary filmmaker whose Communist rebel father was killed by Pinochet's military in 1973, the year he was born.
Some analysts predict that as much as a third of Enriquez-Ominami's supporters will defect to Pinera, even though his alliance of right-wing parties once helped sustain the dictatorship.
"The second round is going to be similar to the last two presidential elections very tight, with the only difference being that for the first time, the opposition candidate has the advantage," said Ricardo Israel, a political scientist at the University of Chile.
Chileans also elected 120 representatives and half of the 38 senators on Sunday.
In exchange for Arrate's support, Frei promised to help Communists into Congress for the first time since Pinochet's 1973 coup. Socialist Rep. Isabel Allende, daughter of ousted President Salvador Allende, was voted into the Senate. But Pinochet's grandson, Rodrigo Garcia Pinochet, lost his congressional race to represent an upscale Santiago suburb.