Manson, who also had the primary assist on the goal by Samuel Girard that made it 2-1, was the unlikeliest of heroes on a night when Blues goalie Jordan Binnington was stopping nearly everything in sight.
Cale Makar couldn't get a shot past Binnington. Neither could Nathan MacKinnon, Gabriel Landeskog, Mikko Rantanen or Nazem Kadri for Colorado, which outshot St. Louis 54-25, including 13-0 in overtime.
So instead it fell to Manson, who received a pass from Landeskog at the right point and faked a shot before his attempt found its way through Landeskog and Blues defenseman Justin Faulk at the top of the crease.
It was Manson's first career playoff goal (27th game).
"That was a nice pump fake up top first that he doesn't get a whole lot of credit for, but that was real nice," Landeskog said. "Got the forward to bite and get a shooting lane. At that point I'm just trying to stand in front and move out at the last second."
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In a way it was fitting for Manson to find the spotlight, to be in the middle of the overtime celebration, after the stay-at-home defenseman struggled a bit after he was acquired in a trade with the Anaheim Ducks on March 14. In 22 regular-season games, Manson averaged 17:24 of ice time but was minus-11.
"I mean, he played his butt off all night long," Colorado coach Jared Bednar said. "It's a great goal, you know, on a great shift. Glad to see him get rewarded."
Manson's importance may not often be celebrated in the headlines, but it is obvious to those that look the hardest.
"I mean, he has been huge for us," Landeskog said. "He's big on the penalty kill, he's a physical presence back there, he's a calming presence in the room. Just a really good teammate, and you can't get enough of those."