Chile’s presidential favourite Michelle Bachelet faces a run-off against her rival and childhood friend Evelyn Matthei next month.
The left-wing former president, 2006-2010, failed to gain an outright victory in the first round or to win a sufficient majority in Congress.
She remains the strong favourite but whether she will be able to implement an ambitious reform programme is uncertain.
Bachelet’s diverse coalition ranges from the Communist Party to the moderate Christian Democrats.
By Monday morning it seemed her bloc had only definitely clinched the simple majority it needs to pass certain planned reforms, including a hike in corporate taxes, the closing of a business tax loophole and the creation of a state-run pension fund.
The bloc was on the cusp of securing the four-sevenths majority required for education reform, a hot-button issue which has triggered massive protests.
However, her Nueva Mayoria coalition had fallen short of the three-fifths necessary to change the electoral system and the two-thirds needed to strike down the constitution which dates from Augusto Pinochet’s military rule.
“The country has voted in the majority for the proposals we have made for Chile, to make Chile once and for all for everyone. The modern, unified and fair country that we all want,” Bachelet told supporters.
Bachelet took almost 47 percent of the vote – nearly twice the 25 percent share of Evelyn Matthei, a minister in the last centre-right government under President Sebastian Pinera.
The electoral system gives the second-place party an inflated presence in Congress.
“This result will surely be disappointing for Bachelet,” said Peter Siavelis, political science professor at Wake Forest University and the author of a book on Chilean politics.
“Social movements that have spilled onto the streets are demanding reform, yet the limits of the institutional structure of Chile are going to limit her capacity to engage in reform.”
Matthei is thought unlikely to gain enough votes from supporters of the seven eliminated candidates to prevent Bachelet from winning the presidency.