The Canadiens (15-5-1), who lead the League with 31 points, have won seven of eight. The lone defeat was a 4-0 loss to the Pittsburgh Penguins on Tuesday.
"You know, these are statement games," Pacioretty said. "We had stretches where we struggled to score goals, and then we come in and score four against a team that doesn't give up many, and that really helps the confidence for us going forward. But I think it definitely makes a statement and shows that we're able to play with the big boys in the [Western Conference]. They're a great team over there and hopefully we opened up a few eyes [Thursday], and now can keep it going."
The Canadiens have six wins when trailing after the first period, the most in the League.
"It's a bit early to be making statements, but it's the type of game that can give you a lot of confidence, especially with the way we played against another strong team Tuesday," Montreal coach Michel Therrien said. "The fun part of the NHL is you get a chance to make up for it. We had that chance tonight, a chance to play against another big team. We had a chance to show we learned something, and that's what we did."
Pacioretty gave Montreal the lead by beating St. Louis goalie Jake Allen on a breakaway at 7:32 of the second period. He scored his second goal of the game, and team-leading 10th of the season, at 6:00 of the third period to put Montreal ahead 3-1.
Pacioretty, whose parents were on hand for this game, scored a hat trick on Nov. 19, 2013 in a 6-2 win against the Minnesota Wild.
"I think I told my parents this is normally a time where I start to heat up, right around my birthday, so I don't want to get too far ahead of myself, but I'm happy to contribute and hopefully I can keep going now," Pacioretty said.
Canadiens forward Lars Eller scored his fourth goal of the season at 12:03 for his first point in five games against his former team.
It was Montreal's first win against the Blues since Nov. 16, 2008, ending a five-game losing streak.
"It always feels good to score, especially against your old team, I'm not going to lie about that," said Eller, who was acquired in a trade from St. Louis on June 17, 2010. "I think it's the first time we've beat them since I've been here, so that was a good feeling. We're going up against some of the top teams and it's a great measuring stick for us and we show that we can play with them when we play to our strengths."
Allen, who played his junior hockey in Montreal, stopped 26 shots in his first game against the Canadiens.
"We haven't been really executing the game plan that we want to bring foreward," Blues defenseman Alex Pietrangelo said. "It's a good hockey club over there. You've got to play your game if you want to beat them. Price came up with some big saves. ... We've got to start taking care of our end and helping out our goalies a little bit more."
Tarasenko and linemates Jaden Schwartz and Jori Lehtera have scored 11 of the Blues' 15 goals in eight road games this season. Nicknamed the “STL Line,” they have 14 goals and 36 points in their past 10 games.
"To me, unless we clean up our own end, it doesn't matter how many goals we score," St. Louis coach Ken Hitchcock said. "So we've got to clean up our own end to start with."
It was the first time this season that St. Louis did not have a power play, and that Montreal did not have to kill a penalty.
Tarasenko's hand-eye coordination was on full display on the opening goal at 7:45 of the first period. Tarasenko swatted at a bouncing puck after Lehtera's pass from the right corner struck Montreal center Tomas Plekanec's stick, and then batted the puck out of midair past Price.
Blues defenseman Kevin Shattenkirk made an ill-advised pass out front that Canadiens forward Dale Weise chopped down to cut off the puck. In his haste to recover, Shattenkirk knocked down Allen as he scrambled out front, leaving Weise a shot into a wide-open right side of the net for his fourth goal 4:50 into the second period to tie the game 1-1.
"That's a nice bounce when you're just standing there, throw your stick up and it hits you," Weise said. "I just kind of made a pump fake, and I saw [Shattenkirk] took his goalie out, so I just tried to get it in there as quick as I could."
PA Parenteau hit Pacioretty with a stretch pass behind Blues defenseman Jay Bouwmeester at the blue line to set up the go-ahead goal. Pacioretty drove in on goal and put a shot between Allen’s pads for his eighth point in his past seven games.
"That was an amazing pass," Pacioretty said. "You know sometimes I try to take away the defenseman's stick; I just had a feeling, though, it was going to land right over it and thankful that it did. Passes don't get much softer and nicer than that, so I credit my first goal to him completely."
Price slid across the goal and stuck out his left pad to deny Lehtera's scoring chance at 4:49 of the third period. He sprawled to stop Schwartz's shot on a pass from Tarasenko on a 2-on-1 at 5:08.
"We made some mistakes on our half of the red line," Hitchcock said. "We made some puck errors that ended up in our net. We got caught on a poor change. [We] gave a big push when it was 2-1. We had all the scoring chances going and then the third one really took the wind out of our sails."
"We don't have any injuries but we all know that you need a lot of depth on defense, and he's a guy that was playing with a good hockey team," Therrien said. "He's got size, he's physical, so we just added some depth with our club."