MANILA - The Philippine Supreme Court on Tuesday ruled that a senator who spent much of her life in the United States is eligible to run for president, reversing a decision by the election commission and putting her in line to reclaim her position as frontrunner.

Voting 9-6, the judges allowed first-term Senator Grace Poe to run in the May election, said court spokesman Theodore Te, a decision that will shake up what is now a tight race to succeed President Benigno Aquino III.

SC: Poe can run for president

Poe, 47, was abandoned as a child in a church and adopted. She moved to the United States when she was a student and settled there.

READ: A foundling named Grace

She had been leading opinion polls, but questions about her citizenship allowed three of her four rivals to catch up.

"This is a victory for the Filipino people, for those oppressed ... a victory for women," Poe told a cheering crowd at an international women's day celebration at a park in Manila.

"Women's role goes beyond looking after homes, we can do a lot of things. Let's make 2016 the year when women triumph in government."

Aquino, in power since 2010, is barred under the constitution from seeking a second term.

The election is being closely watched by investors who fear the political succession could derail average economic growth of more than 6 percent a year and derail efforts to crack down on corruption made under Aquino.

Aquino's chosen successor, former interior minister Manuel Roxas, is lagging behind in opinion polls, coming third behind Poe and Vice President Jejomar Binay, who was in a statistical tie with Poe in the latest independent poll.

Poe has campaigned on a pro-poor campaign, promising to build on Aquino's programs of creating jobs and building infrastructure, which have helped propel one of Asia's fastest growing economies.

"It's a dangerous result," Manuelito Luna, a lawyer for former senator Francisco Tatad who opposed Poe's candidacy, told Reuters. "It's a recipe for chaos."

Luna said his team would appeal against the decision.

Ramon Casiple, executive director of the Institute for Political and Electoral Reform, told Reuters the ruling would put her back in the lead.

"A favorable decision seals Poe's frontrunner position," he said.

Edmund Tayao, a political science professor at Catholic-run University of Santo Tomas, said the court ruling could boost Poe's numbers by at least 10 points, boosting her chances of winning the May vote.

"This might not be not on the same level of a black swan as it was in 2010 when democracy icon Cory Aquino died, but it could be a game changer," Tayao said, referring to the landslide victory of Aquino after the death of his mother, who had also been president.

A spokesman for Binay said the court ruling "has no bearing on our campaign."

Poe, a former teacher, spent much of her adult life in Fairfax, Virginia, marrying an American of Philippine origin.

She returned to the Philippines in late 2004 after her adoptive father, action movie hero Fernando Poe, died and topped the Philippine senatorial race in 2013, running on his legacy.

Election officials had disqualified her on the grounds that she had failed to meet a 10-year residency requirement.