Mayhem erupted in Williamsburg last night at a post-Dominican Parade block party, where one man was stabbed, another was assaulted and COPS HAD TO USE PEPPER SPRAY TO BREAK UP A separate BRAWL.

“It was a big riot,” said Elias Rodriguez. “Crazy, crazy times.After 9 [p.m.], everyone just started going crazy.”

First, a melee broke out between two groups at South Fourth and Keap streets. One man suffered a knife wound to the hand, and another was smashed in the head.

“It started as a 12-on-12 brawl, then cops came to break it up,” said witness Mario Delgado.

About an hour later, two women got into a fight a block away, on Hooper Street.

Cops had to use pepper spray to break it up, officials said. Three people were taken into custody.