Chicago voters on Tuesday signaled a strong break from decades of machine politics, choosing a black gay woman and former prosecutor to be the city's next mayor.

Voters overwhelmingly chose Lori Lightfoot, an attorney who once worked to root out corruption in Chicago's Department of Procurement Services but who had never held public office before.

She beat out Toni Preckwinkle, the president of the Cook County Board of Commissioners, a veteran politician who also runs the Cook County Democratic Party. With two-thirds of precincts reporting, Lightfoot held 74 percent of the vote.

Lightfoot is the first woman to win the mayoralty since Jane Byrne in 1979. She is the first African-American to win the office since Harold Washington in 1983. And she is the first openly gay woman to win the office.

The race between two black women — and the crowded field they beat out in the first round of voting — became a referendum on the city's long history of corruption and machine politics. Weeks before voters went to the polls in February, Chicago's longest-serving alderman, Edward Burke, was arrested and charged with attempting to extort a small-business owner.

Virtually every major candidate in the race had ties to Burke. Preckwinkle had benefited from a fundraiser at his house and hired his son. Another candidate had worked for him in the past, and a third got married at his home.

Lightfoot was the only significant candidate in the race without a connection to Burke.

"Nobody owns Lightfoot in the political game," said Gregory Seal Livingston, a civil rights activist and interim pastor at the New Hope Baptist Church.

As the scandal mushroomed and other candidates raced to distance themselves, Lightfoot came to embody a different path for Chicago. That she beat Preckwinkle, who runs the second-largest Democratic organization in the state, put an exclamation point on voters' option to break with the past.

"This is seen through the lens of a change election," said Richard Boykin, a former Cook County commissioner who backed Lightfoot. "I hope and pray that the machine is on life support. That way of doing business hasn't been helpful to the citizens of Chicago."

In the initial round of voting, Lightfoot won many precincts in Chicago's northern neighborhoods, where white liberals and wealthier voters tend to live. Preckwinkle advanced to the runoff on the strength of her performance in the city's western and southern neighborhoods, home of Chicago's large black population; Preckwinkle finished second among those voters, trailing philanthropist Willie Wilson in many wards.

Lightfoot will be inaugurated in May. She is likely to find a handful of new allies on the city council, where at least eight new aldermen have already won election. Several runoff elections held Tuesday were also likely to send new members to City Hall.

But in a sign of the machine's staying power, a familiar name will greet Lightfoot when she is sworn in. Ed Burke won reelection in his ward in February, a month after he was indicted, with 54 percent of the vote.