The Bruins had grand plans.

They would win on Tuesday night, beating a very good Blues team in their second game of a back-to-back, and Montreal would lose to Minnesota. Boston would then head into the three-game Christmas break in first place in the Atlantic Division, a thought that would have been laughable at the beginning of the season.

Montreal kept its end of the bargain, losing its fifth straight, but the Bruins couldn’t quite keep theirs.

They came close, maintaining a scoreless tie into the third period.

But Blues winger Vladimir Tarasenko got through defensemen Dennis Seidenberg and Colin Miller and wristed a shot gloveside on Tuukka Rask, beating the goaltender at 7:35 of the final frame. It proved to be all St. Louis needed in a 2-0 victory at TD Garden.

For the Bruins, it meant an end to a 15-game run in which they had gone 11-1-3, vaulting them higher and higher in the standings. But the Blues had been one of their tougher matchups of late, a game that would help let them know where they stood in the NHL’s hierarchy. And the Bruins mostly stood up to the challenge.

“I thought for two periods we were fine, but at the end of the night I think the biggest thing is that I didn’t think we worked hard enough to get on the inside,’’ coach Claude Julien said. “They did a good job of keeping us on the outside. There’s a lot of times we were shooting and we had no net-front presence. They were boxing us out and we weren’t working hard enough to get on the inside. Same thing on some of those rushes.’’

Still, the Bruins had kept the Blues off the board. They had a few chances, with Jake Allen (32 saves, tied for league lead with five shutouts) making some crucial saves, especially on Loui Eriksson and Brad Marchand, to stymie Boston. Tuukka Rask (27 saves) did what he needed to on the other end.

“After two periods, I think it’s a pretty even game, it’s a chess match,’’ Julien said. “They got a break there with their most dangerous guy on a breakaway, Tarasenko, opened up the scoring and that was probably the thing that stung the most.’’

On the Tarasenko goal, Miller had rimmed the puck around the boards in the offensive zone, but Eriksson couldn’t gain possession, nor could David Krejci, and Blues center David Backes ended up with it. He sent the puck to Magnus Paajarvi at the blue line, and Paajarvi found Tarasenko, who got ahead of the Bruins defense.

“Somehow it went through two guys and I followed up and they just kind of took off,’’ Seidenberg said. “I don’t know. A couple of tough bounces over a couple of sticks and the rest is history, I guess.’’

Said Miller, “He’s got a lot of speed and he kind of busted through the middle there. I was just trying to get it deep and it went through a couple guys there and bounced out. He came up the middle there and he had a lot of speed and he just kind of slithered through there.’’

The Blues added another goal with 7:10 left, a Robby Fabbri shot from the left faceoff dot on another breakaway.

“Just a couple breakdowns,’’ Marchand said. “I didn’t think we had a bad period other than a couple breakdowns on those goals. We had a couple chances that we didn’t capitalize on, and that’s just how hockey is sometimes.’’

Those two goals were all the Bruins allowed to the Blues in a game that was a measuring stick. As Seidenberg said, “We have some work to do, but overall I think we can take positives out of it and go from there.’’

So instead of heading into the break up by a point, the Bruins will celebrate the holidays 1 point behind Montreal. Of course, they still have three games in hand, not exactly a bad place to be at this point in the season.

“We’ve taken a lot of strides forward and we definitely have to build on that and realize what we’ve done,’’ Patrice Bergeron said. “But at the same time I think we can’t be satisfied and it’s games like tonight that we have to keep getting better and finding ways to win those type of games because that’s the type of hockey you play in the playoffs.’’

Amalie Benjamin can be reached at abenjamin@globe.com. Follow her on Twitter @amaliebenjamin.