Dustin Brown and Jeff Carter scored for the Kings (9-8-5), who lost their fourth straight after a six-game winning streak. Cal Petersen made 19 saves.
"I think it's a good lesson for us as a group," Brown said. "Maybe [during the] six-game winning streak, we squeaked out a couple games where bounces went our way. It's a good lesson to learn, you're going to have to play a full 60 to get out of this little skid we're in. A lot of good things we can take from this game, but it is a frustrating loss."
The teams will play again here Saturday.
Perron tied it 2-2 with a wrist shot from the right circle after the Kings were caught in transition trying to score with Husso pulled.
Hoffman helped set up the goal by beating Los Angeles center Anze Kopitar to a puck that was headed toward the open net, then backhanding it to O'Reilly, who passed ahead to Perron in the neutral zone. It was St. Louis' seventh 6-on-5 goal this season.
"Just finding ways to win games," Blues coach Craig Berube said. "I think we have played some good hockey. It's not great. We don't panic, stay calm and come around to get a goal. It's really a team goal and contributing to help out."
The Blues are 10-2-0 on the road and have won the first four of a six-game trip.
"It is just the way it is going right now," Perron said. "We play the same every night."