The Bruins (45-17-10) joined the Tampa Bay Lightning from the Eastern Conference. The Nashville Predators are the only team to secure a spot in the postseason from the Western Conference.
"Getting that goal, getting that one playoff point, it's huge for us," said Bruins forward Ryan Donato, who scored his second goal in his second NHL game. "Obviously, this wasn't the result we wanted, but we're where we want to be."
WATCH: [All Bruins vs. Blues highlights\]
Jaden Schwartz scored 30 seconds into overtime to give the Blues their third win in a row, fifth in six games, after he tied it 1-1 at 9:36 of the third period.
Schwartz won the game when he collected the puck from defenseman Colton Parayko behind the Blues net, moved up through the middle of the ice, and used Bruins defenseman Matt Grzelcyk as a screen to beat goalie Anton Khudobin (18 saves) with a wrist shot low to the stick side.
"Colton gave it to me behind the net, and I knew I had some space, just tried to pick up some speed and see what was going to develop," Schwartz said. "The one guy kind of went with [Brayden Schenn]. I kind of had a little 1-on-1, just tried changing the angle and getting it through the guy's legs."
St. Louis (40-29-5) is two points behind the Los Angeles Kings for the second Western wild card into the playoffs and three behind the Colorado Avalanche for the first wild card.