The monster who fatally stabbed a couple’s dog in Central Park pulled a switchblade after his three unleashed pit bulls attacked the doomed pup, police sources told The Post Sunday.

The vicious attack Saturday night happened as the helpless dog’s owners scrambled to separate the animals near the park’s 106th Street and East Drive entrance, sources said.

The suspect’s trio of pooches were not on leashes when they charged after Eli, a female pit bull-German shepherd mix, around 8:30 p.m., who was being walked by a couple from the area, according to sources.

The pair also had a Chihuahua with them.

The dog fight sparked an argument between the three owners, and that’s when the brute — wearing an orange hat, gray shirt and blue jeans — allegedly stabbed Eli to death, sources said.

He fled the park with his pets.

Eli’s owners rushed her to the vet but she had to be euthanized.

The chihuahua wasn’t hurt.

Cops say they’re canvassing the area and are still investigating the killing. No arrests have been made.