Mayor de Blasio took the stage 25 minutes late for a Democratic candidates’ forum Tuesday night where long-shot rivals criticized him on everything from his handling of homelessness to schools to policing.

De Blasio was scheduled to speak at 8:30 pm at the forum, sponsored by the Village Independent Democrats political club, but arrived at the LGBT Center in the West Village about 18 minutes late.

He took the stage at 8:55 p.m. His campaign announced around noon Tuesday he would be attending the event, but staffers declined to offer an explanation for his tardiness.

De Blasio faced off against four long-shot challengers at the forum: businessman Michael Tolkin, police reform advocate Robert Gangi, former City Councilman Sal Albanese and Kevin Coenen, a retired FDNY firefighter.

They didn’t waste time attacking him on his handling of Corrections Department Commissioner Joe Ponte’s personal use of a city vehicle or the corruption probes that dogged de Blasio throughout much of 2016.

“Pay-to-play corruption is rampant and very little effort is being done to mitigate it,” said Albanese, citing probes of Team De Blasio from the Manhattan DA and US Attorney’s Office. Both investigations have been closed with no finding of wrongdoing against the mayor.

Gangi slapped at de Blasio’s efforts to cut marijuana arrests and hammered the administration on class size in public schools.

“There is no commitment on the part of the de Blasio administration – or any previous administration – to provide smaller classes in our schools. That would be a major priority for my administration,” he said.