It took less than five minutes for Chicago’s two mayoral finalists to get under each other’s skin Thursday night in the first debate of the April 2 runoff election, clashing sharply over their credentials to lead the city.

Cook County Board President Toni Preckwinkle and former Chicago Police Board president Lori Lightfoot showed little in the way of major policy differences during the one-hour event hosted by NBC 5 and Telemundo Chicago.

But the pair of self-styled progressives made it clear that they wouldn’t trust one another to be Chicago’s next mayor.

The arguments heated up as soon as moderator Carol Marin asked Lightfoot about Preckwinkle’s criticism that she is a political insider as a partner in the Mayer Brown law firm and as an appointee in the city administrations of both Richard M. Daley and Rahm Emanuel.

“I think it’s interesting and frankly disappointing that Toni Preckwinkle and her people would try to criticize me for being successful,” Lightfoot said, referencing her working class roots. “I am a black success story, as are many people who are in the middle class and upper middle class of this city.”

“I’m not a person who decided that I would climb the ladder of the political party, the corrupt political party,” Lightfoot said. “I don’t hold the title of committeeman, central committeeman, boss of the party.”

“One thing I am is a person who took on Rahm Emanuel. I didn’t stand on the sidelines until Goliath was slain,” Lightfoot added, a reference to her declaring her candidacy before Emanuel announced his decision to not seek re-election, unlike Preckwinkle.

Preckwinkle fired back: “I grew up poor, too. That’s not the point. The point is what you choose to do with your time and talent as a result.”

Preckwinkle, who has been an elected official since 1991, then touted her credentials as a former school teacher and non-profit leader, comparing that to Lightfoot’s “equity stake” in a law firm that “defends Big Tobacco, that defends Big Pharma, that defends environmental polluters.”

Lightfoot tried to interrupt, which led to the two candidates shouting over each other until Marin broke it up and allowed Preckwinkle to resume the attack.

“The question is not that you’re successful. It’s possible to be very successful and not be an equity owner in a firm that has a history of protecting the privileged and the powerful against working people, against working families,” Preckwinkle said.

Lightfoot demanded a chance to respond.

“I wondered what level of nastiness and hypocrisy that you were going to bring to this discussion, rather than talk about the issues that I think are important to voters all across the city,” she said.

Lightfoot then noted that Preckwinkle just took a $2,500 campaign donation from one of her law firm’s partners.

“If we were so awful, why were you constantly soliciting donations to your campaign from partners at Mayer Brown? That’s the height of hypocrisy,” Lightfoot added.

The discussion heated up again later when Preckwinkle answered a question about what she would do to protect Chicago’s sanctuary city status by accusing Lightfoot of accepting the endorsement Thursday of two aldermen who she says support President Donald Trump and who voted against the city providing legal aid to undocumented immigrants — Nicholas Sposato (38th) and Anthony Napolitano (41st).

Marin asked Lightfoot to respond, but Preckwinkle insisted on continuing.

“Okay, you lie, and then I’ll respond,” Lightfoot said. “There’s no lie you will not tell.”

“You know, I’m not accusing you of lying,” Preckwinkle said.

Marin then asked for a “timeout,” which was only long enough for the candidates to take a deep breath.

Lightfoot accused Preckwinkle of telling “lie after lie.”

“I’ve heard a lot of craven things in politics, but man, you are shameless,” she continued.

Lightfoot then argued that she had accepted the endorsement of Chicago Firefighters Union Local 2 and that the two aldermen “showed up” because they are union members. She said she has been highly critical of both aldermen.

“When someone stands with you, it’s hard not to take that as an endorsement,” Preckwinkle said, then criticized Lightfoot for “name calling.”