Binnington, who allowed four goals on 85 shots in the first two games of the series, sustained the injury at 6:45 after he was knocked over by teammate Calle Rosen and Avalanche forward Nazem Kadri, who was skating hard for a rebound.
"I just see a loose puck, really," Kadri said. "I mean, I was kind of just sitting behind him and just tried to poke it with my stick, and I think their defenseman kind of collided with me and pushed me into him. So you know, had that not been the case, I don't think I would have hit him at all. It's a loose puck. I'm just trying to bang it in."
St. Louis, which was coming off a 4-1 win in Game 2, was leading 1-0 at the time of the injury.
"It's always tough," Blues captain Ryan O'Reilly said. "Obviously, 'Binner's' the heart and soul, playing unbelievable, but I think it kind of took the momentum away and took us a little too long to kind of get it back going again. Things like that happened. We're a deep team, and we could have done a better job of getting the momentum back and adjusting."
RELATED: [Complete Avalanche vs. Blues series coverage]
Artturi Lehkonen scored twice, Kadri had a goal and an assist, and Darcy Kuemper made 29 saves for the Avalanche, who are the No. 1 seed from the Central Division.
"I thought we were a little tentative out of the gate," Colorado coach Jared Bednar said. "And then as we kind of got playing a little bit, just every minute got a little bit better and got ourselves into the game. Not the ideal start you want. You could sense a little nervousness, but I give our guys a lot of credit for playing through that. Darcy came up with some big saves for us when we needed them tonight, because we had some breakdowns, especially at the end of the second."