Police said a 73-year-old St. Louis man was in his garage Tuesday afternoon when a pair of armed men approached him, KSDK-TV reported.
One of them put a gun to the homeowner's head and ordered him to back up, police said.
But at that point the homeowner pulled his own gun from his pocket and shot both intruders, police said, adding that they were after the homeowner's vehicle.
Jonathan Warren, 18, of Florissant and Lonnie Middlebrook, 20, of Ferguson were pronounced dead at the scene of the shooting, KDSK said.
Authorities said Warren's gun was reported stolen Oct. 30 by Florissant Police, KMOV reported. Both intruder's were armed, the station added.
A neighbor of the homeowner said he and his wife are well liked.
"You just kind of see them come and go ... when the weather was nice, they were out," Kim Bryant told KMOV. "They are nice people."
KDSK said homicide detectives are investigating and police indicated it looks like a case of self-defense.