Nathan Walker made it 4-2 at 9:29 of the third period after a block shot bounced to him on the other side of the slot.
Pettersson scored at 15:11 to make it 4-3 on a deflection in the slot, but with 1:10 left and Demko pulled for an extra attacker, Husso robbed Tanner Pearson from the slot with his glove.
"We know how important every game is now and we're not going down without a battle," Pettersson said.
NOTES: Vancouver forward Bo Horvat left after the first period because of a non-COVID related illness. "He's got 26 goals, he's your captain, he kills penalties, he plays the power play," Boudreau said. "Five minutes before the game, I'm hearing he's sick but he's going to try it and then you lose him, so all of the sudden you're mixing and matching for the rest of the game, especially with some of the young guys we have in, mixing and matching isn't as easy as it sounds." … Forward Jordan Kyrou, who leads St. Louis with 62 points (22 goals, 40 assists) in 61 games, was a late scratch with an illness but there was no update after the game. … "We'll see how he is tomorrow," Berube said. … St. Louis center Logan Brown played 7:14 after being added late to the lineup because Kyrou couldn't play. … Blues defenseman Robert Bortuzzo had two hits and a blocked shot in 11:52 after being a healthy scratch against the Canucks on Monday. … Richardson's assist was his first point in five games since being claimed by Vancouver off waivers from the Calgary Flames on March 21. Petan's assist was his first point in nine games with the Canucks this season.