The new UC Berkeley Institute of Governmental Studies poll puts Rep. Karen Bass ahead of businessman Rick Caruso - 34% to 31% among all voters.
Caruso is now just 3 points behind -- which is within the poll's margin of error. In August, Caruso trailed by 12 points.
Among likely voters, Bass still leads by 15 points - 46% to 31%.
Caruso's campaign released a new ad last week called "Church of Karen," which takes a speech that Bass, delivered in 2010 at a Church of Scientology event and intersperses it with negative headlines about the controversial church.
Karen Bass, Rick Caruso square off in Los Angeles mayoral debate
"It's ridiculous to associate me with the Church of Scientology," Bass told ABC7. "I am a Baptist. My minister is Norman Johnson and I have never ever been affiliated with scientology and absolutely condemn their practices."
Caruso said he believes Bass is hiding something in connection with a recent burglary her home, in which two guns were stolen and two people were arrested.
"Why doesn't she tell us what kind of guns they were?" he said. "We got two more guns on the street now. We have the highest level of gun violence. Why doesn't she show us the box that they were kept in? She says it was pursuant to L.A. city law, well, prove it. You've got an obligation. You're running for mayor."
Bass responded by saying, "I think that Caruso knows better than this, and to be someone who had my house robbed and to have my opponent turn it on me as though I am the criminal, is kind of pathetic."
Ballots will be mailed out starting Thursday. Election Day is Nov. 8.