PORTLAND, Ore. -- A man who intervened in an altercation in downtown Portland Sunday evening was stabbed by a stranger and then protected by witnesses, court records show.

Aaron Moore, 22, was walking with his girlfriend on West Burnside near Stark Street just before 7 p.m. when he saw 30-year-old Portland resident Matthew Allen Davis yelling at some women and throwing things at them.

Moore's girlfriend told Portland police detectives that Moore began arguing with Davis, court records show. Davis then allegedly slashed Moore's arm with a knife and began chasing him. Moore fell to the ground and Davis attacked him again.

A TriMet bus driver at the scene told detectives Davis stabbed Moore another time before some good Samaritans stepped in.

"Other good Samaritans intervened and got Davis off of Moore and held him for police," said Portland police spokesman Sgt. Pete Simpson. "An unidentified person pepper sprayed Davis during the struggle to hold him down."

Officers at the scene found Moore suffering from a serious stab wound and they applied a tourniquet as they waited for medical personnel to arrive. He was taken to a Portland hospital and is expected to survive his injuries.

Davis told detectives he tried to punch Moore after he "swung first."

"When asked if he stabbed the victim, the defendant denied it and could not explain how the victim sustained his knife wounds," the detective reported.

Davis lives alone in an apartment in Old Town, records show. He was booked on an assault charge and is being held on a $255,000 bail.

In 2012, Davis was convicted of giving liquor to a minor and trespassing.

The attack comes one month after a deadly MAX attack in Northeast Portland. Three men intervened when suspect Jeremy Christian verbally attacked two young women on a train. Christian stabbed two men, Rick Best and Taliesin Namkai-Meche, to death, and injured Micah Fletcher.

Portland MAX attack: What we know