MEXICO CITY — As accusations of fraud swirl around the presidential race, there is one Mexican election that is undisputed: the victory of Miguel Angel Mancera, the capital city’s mayor-elect.

The soft-spoken legal scholar, who until recently was the city’s top prosecutor, won with 63 percent of the vote.

Mancera was the candidate of the Democratic Revolutionary Party, or PRD, which has run Mexico City since 1997 and is credited with transforming the colossal capital from urban dystopia to tourist destination.

It was a remarkable political debut, but it was viewed mostly as a show of the Mexican left’s strength.

“The left could have picked a name randomly from the phone book and won the mayorship,” said George Grayson, a professor at the College of William and Mary.

Under PRD governance, air pollution has been reduced by half. The public pedals city bicycles, which share the streets with low-emission buses and experimental hybrid electric public vehicles in the Federal District, or D.F., an entity similar to the District of Columbia.

Attention to quality of life has brought concerts by Paul McCartney and Justin Bieber in the downtown Zocalo square; one of the world’s largest ice-skating rinks; and free Viagra. The elderly and single mothers receive pensions, and there is free medical care for the uninsured.

The PRD-dominated city assembly has legalized gay marriage, no-fault divorce, abortion and, in some cases, euthanasia, priding itself on being in the vanguard of social tolerance in a conservative Roman Catholic country.

“Ours is a city of liberties, a city of consolidation of rights,” Mancera said in an interview at his campaign headquarters, in a modest office building in a leafy neighborhood in the south of the city. “It is a city that fights against gender discrimination and for the protection of women. Here is where the decriminalization of abortion was first discussed, where same-sex marriage is permitted.”

“It is a city that opens paths of modernity that make their way to other cities,” he said. “It is a jumping-off point.”

In a country convulsed by the drug war, Mexico City is also an island of relative safety. As murder, kidnapping and robbery rose in the rest of Mexico, Mancera campaigned on a 12 percent reported decline in crime here between 2010 and 2011, while he was the city’s attorney general.

Mexico City analyst Ana Maria Salazar said Mancera is perceived as a charismatic, highly intelligent “un-politician” who quietly rose with popular outgoing Mayor Marcelo Ebrard by helping to solve the security problem.

“In six years, Ebrard was able to convert Mexico City from being known as one of the most dangerous capitals of the world to one of the most innovative and progressive. You could not change the image of Mexico City until you dealt with the security issue,” said Salazar, who is also a television and radio anchor. “That’s where Miguel Angel Mancera came in. He was a fundamental part of Marcelo Ebrard’s success as a mayor.”

Looming challenges

The PRD’s most significant task is achieving environmental sustainability in one of the world’s biggest cities.