* Center-left Bachelet promises tax, education reform
* In Chile first, two women are president front-runners
* Matthei, Bachelet have known each other since childhood
Former President Michelle Bachelet is virtually guaranteed to win Chile's election runoff on Sunday and the center-left leader is gunning for a landslide triumph to bolster her reform mandate.
In Chile's first presidential showdown between two women, voters are expected to give overwhelming backing to Bachelet, who led the country from 2006 to 2010, impressed by her easy charm and plans to tackle deep income inequality.
Her right-wing rival, the sharp-tongued Evelyn Matthei, has been weakened by her family's ties to the 1973-1990 military dictatorship of General Augusto Pinochet and by her post in the unpopular government of outgoing President Sebastian Pinera.
In the first round of voting on Nov. 17, Bachelet, a 62-year-old pediatrician by training, won nearly twice as many votes as Matthei, a 60-year-old economist and former labor minister. But Bachelet fell just short of the 50 percent needed to win outright, pushing the vote into a runoff.
The two women were playmates during their childhood on an air force base, though the bloody 1973 military coup later divided their families.
"This is not about choosing between 'two women', as the press likes to put it," Bachelet said in a closing campaign speech to hundreds of cheering supporters on Thursday.
"There are deep differences here. I think Chile is ready to face the transformations that will allow it to be the country we all want. We can turn Chile into a truly developed country."
Robust, copper-led economic growth has turned Chile into a Wall Street favorite, but many Chileans feel they have yet to see the fruits of the mining boom as wealth and power remain largely concentrated in the hands of a small elite.
Bachelet wants to hike corporate taxes to pay for a wide-ranging education reform, shred the dictatorship-era constitution, and legalize abortion under certain circumstances.
There have been no major polls ahead of the run-off, mainly because Bachelet's victory has been taken for granted.
While there is little doubt about the overall outome, analysts say this assumption could result in voter apathy and low turnout that could deny Bachelet the dramatic win she is looking for to pressure a notoriously tricky Congress to approve her reforms.
"People are tired and disaffected, and that will be obvious in abstention levels," said Pablo Salvat, professor at the Alberto Hurtado University. "It could be that fewer people vote than in the first round."
Bachelet's support is strong among lower and middle-class women, while Matthei's backing is higher among older and wealthier segments of the population.
Still, in percentage terms Bachelet, could clinch the biggest share of the vote since Chile's return to democracy.
Bachelet and Matthei were neighbors during their childhood on a base in northern Chile, where their fathers were air force general who became close friends.
The girls rode bikes and played together in the street, according to a bestselling book about them.
But the military coup that ushered in the 17-year long Pinochet dictatorship affected them very differently.
Matthei's father became a key member of Pinochet's junta while Bachelet's father, loyal to deposed socialist President Salvador Allende, was arrested, tortured by Pinochet's agents and died in prison.
Bachelet and her mother were also tortured before fleeing into exile.
Matthei backed Pinochet in a 1988 plebiscite about his rule, a decision that has dogged her in this election campaign just as Chile commemorated the 40th anniversary of the coup.
In her closing campaign event on Thursday, Matthei linked Bachelet's reform drive to the far-left government of Venezuela.
"They want to change the constitution to resemble Venezuela, where every day it's harder to find food," Matthei said. "Does that remind you of anything?," she added, in an apparent reference to shortages of the Allende era.
She and Bachelet are not friends nowadays, though their connection was clear during a televised debate on Tuesday, when they referred to each other by their first names and the informal Spanish form of "you."
Chileans can vote from 8 a.m. local time (1100 GMT) to 6 p.m. (2100 GMT). Results are due shortly after voting ends.