Susan Kuhnhausen, 51, then ran to a neighbor's house Wednesday night to report the intruder, identified as Edward Dalton Haffey, 59, whose body was found by police.
An autopsy by the Multnomah County medical examiner determined the cause of death to be strangulation, said Officer Catherine Kent, a spokeswoman for the Portland Police Bureau.
Homicide detectives were investigating, Kent said.
Police say there was no obvious sign of forced entry at the house when Kuhnhausen, an emergency room nurse at Providence Portland Medical Center, got home from work shortly after 6 p.m.
Haffey, a convicted felon with a long police record, was dead when police arrived.
"Everyone that I've talked to says 'Hurray for Susan,'" said neighbor Annie Warnock, who called 911.
Under Oregon law people can use reasonable deadly force when defending themselves against an intruder or burglar in their homes.
"You didn't need to calm her," Warnock said. "She's an emergency room nurse. She's used to dealing with crisis."
Kuhnhausen was treated and released for minor injuries at Providence.
Haffey, about 5 foot 9 inches tall and 180 pounds, had convictions including conspiracy to commit aggravated murder, robbery, drug charges and possession of burglary tools.
Neighbors said Kuhnhausen's size - 5 foot 7 inches tall and 260 pounds - may have given her an advantage.
Paula Derr, a LifeFlight nurse, said Kuhnhausen has been an advocate for protection of nurses, who sometimes face violence in the workplace.
(Copyright 2006 by The Associated Press. All Rights Reserved.)