St. Louis defenceman Eric Brewer was serving a double minor for roughing and the Canucks took advantage of the 4-on-3 situation, with Sedin tapping in the puck from the side of the net for his 31st goal of the season.
The goal came on Vancouver's lone power-play chance of the game and ended a 0-for-19 slump that spanned four games.
Vancouver netminder Roberto Luongo stopped 20 shots to become the 20th goalie to record 40 wins in a season. The Canucks have 11 regular-season games remaining, meaning Luongo could have a shot at the NHL record of 47 wins, set by Bernie Parent of the Philadelphia Flyers in 1973-'74.
Vancouver (41-23-6) earned its first win in three games to remain a point ahead of the second-place Minnesota Wild, who defeated Edmonton 2-1 on Thursday.
St. Louis (29-29-12) slipped to 22-12-8 under head coach Andy Murray after suffering its fifth loss in six games and third in four contests against Vancouver.
Trevor Linden and Henrik Sedin gave Vancouver a 2-0 lead before the Blues rallied in the third period on goals by Jamal Mayers and Petr Cajanek.
The Blues tied the game with 3:25 remaining in the third when Cajanek scored on a goal-mouth scramble in front of Luongo. Earlier, Mayers's shot from a sharp angle found a way past Luongo.
It marked the second time in as many games that Vancouver surrendered a two-goal lead in the third.
Henrik Sedin put Vancouver ahead 1-0 when he took brother Daniel's pass inside the St. Louis blue-line, beat defenceman Matt Walker with a spin move before firing a shot past goalie Curtis Sanford.
It was the second goal in four games for Sedin, who had an overtime winner against the San Jose Sharks on March 9.
Linden ended a nine-game goal-scoring drought when he converted a Brendan Morrison pass, forcing St. Louis was forced to open up the game in the third.
Sanford, who got his last shutout against the Canucks more than a year ago, was forced to make some solid saves. He stopped Bryan Smolinski three times, once on a 2-on-1 break and twice with his right pad. He also denied Daniel Sedin's attempt to convert a rebound and stood his ground to stop Mattias Ohlund.
Sanford kept his club in the game in the second with another good save on Smolinski and a glove stop off Jeff Cowan while Canuck Alex Burrows hit the post.
NOTES:Willie Mitchell (groin) was out of the Canuck lineup for a second straight game . . . Vancouver returned Nathan Smith to the AHL's Manitoba Moose after a one-game callup . . . Defenceman Rory Fitzpatrick missed Wednesday's practice with the flu but played against the Blues . . . The Canucks are at home Saturday to Detroit, the NHL's top team, but former Vancouver forward Todd Bertuzzi (back) won't play for the Red Wings . . . Smolinski, obtained by Vancouver at the trading deadline, faced the Blues for the 10th time this season.