ST. LOUIS -- One of the NHL's top goalies made a key mistake.
Andy McDonald and Patrik Berglund scored power-play goals for Louis and Alexander Steen scored when Luongo didn't get all of the puck and wound up slipping it right to Steen, who made it 2-1 at 12:17 of the first.
"The puck was coming towards me and I thought I had enough time to shove it over there," Luongo said. "Obviously, it was a bad decision. He anticipated it and made me look pretty bad."
St. Louis won for the third time in the last 10 games. Vancouver lost for the second time in nine games.
St. Louis had scored just once in 12 previous power plays, but went 2 for 5 on Monday. Vancouver had killed off 36 straight penalties before McDonald connected at 5:10 of the first period for a 1-0 lead.
Henrik Sedin tied it before Steen, who had not scored in his previous 11 games, capitalized on his gift.
"I thought it was just a lucky play," Steen said. "He kind of fanned on it."
Berglund added a man-advantage goal late in the second period to make it 3-1.
"We got a lot of PP time and we were shooting and putting pucks on the net," Berglund said. "We'd been struggling. This was a huge win for us. The top team in the league in our building, obviously it was great to get these two points."
Luongo had a 21-game regulation unbeaten string snapped. He came in with a 16-0-5 mark and had won his previous six starts.
St. Louis defenseman Alex Pietrangelo assisted on both power-play goals.
Vancouver bounced back from McDonald's goal to tie it 1-1 on Sedin's 13th tally of the season. Alexandre Burrows assisted on the goal to extend his point streak to 10 games, the longest current one in the league. Burrows has eight goals and four assists over the 10 games.
"I thought we played a real strong third period," Vancouver coach Alain Vigneault said. "We had a pretty good push. But their goaltender made a couple of outstanding saves."
The Blues, with 59 points, moved to within six points of Minnesota for the eighth and final playoff spot in the Western Conference.
"I think the desperation was there," Blues coach Davis Payne said. "It was five guys going over the boards, making sure they made the right plays. A big step for our club."
St. Louis D Barret Jackman played in his 500th career game. ... St. Louis has sold out all 29 home games this season. ... Vancouver's Henrik Sedin has a league-best 55 assists. ... The Canucks still lead the NHL with 81 points. They have never held the top spot in the standings this late in the season.