An unarmed hotel security guard was the first person to find and attempt to stop Las Vegas mass shooter Stephen Paddock — and his bravery likely saved countless lives, according to a new report.

Mandalay Bay ​security ​guard Jesus Campos was carrying just a nightstick when he tried to open Paddock’s barricaded door on the hotel’s 32nd floor Sunday night, the Daily Beast reports.

Paddock, who had cameras looking outside his room, stopped shooting at the crowds below and fired through the door at Campos, blasting him in the right leg.

Campos immediately called in to the casino’s dispatch to report on the shooter’s location — and other guards and cops were then able to rush to the location and draw Paddock’s fire.

“We would not have engaged this individual in the time lapse we did without [the security guard​’​s] assistance,” Las Vegas Sheriff Joseph Lombardo told the news outlet.

Paddock ultimately turned his gun on himself, and was found dead an hour later after a SWAT team stormed his room.

Very few security guards at the casino and hotel complex are armed, and Campos and others deserve accolades for rushing into the line of fire to stop the killer, said a union rep for the workers.

“We just want to make sure that Mr. Campos and all of our officers are recognized for what they do every day, which is protect people,” Dave Hickey, president of the International Union, Security, Police and Fire Professionals of America, told the Daily Beast.