Halak, traded to St. Louis by Montreal last summer, made 27 saves Thursday night to lead the Blues to a 4-1 victory against the Canadiens at a sold-out Scottrade Center.
"It was an emotional game for me," he said. "I spent a few years in Montreal, and especially last year, we went so far in the playoffs. It was a great run, and I had a lot of fun there. But this is my new home, and I'm happy to be here."
Halak led the Canadiens to upset wins against Washington and Pittsburgh in the Stanley Cup Playoffs last spring, but the Habs opted to go with Carey Price as their starter and traded Halak to the Blues.
He said he still has a lot of friends on his former team -- now that the game is over.
"During the game, you just want to focus on hockey. You don't want to think about the friends on the other side or ex-teammates," said Halak, who stopped the last 22 shots he faced after Jeff Halpern scored midway through the first period.
"Obviously, when you play for a team and then you get traded, you want to beat them every time you play them," Halak said. "We play Montreal only once a year, so that was my chance this year. I needed to make sure I gave it my best.
Montreal was playing its first game without forward Max Pacioretty, who's out indefinitely with a severe concussion and fractured fourth vertebra as a result of a check by Boston defenseman Zdeno Chara on Tuesday.
"You're concerned about him, but at the end of the day, we're professionals," Canadiens captain Brian Gionta said. "We're going to go out there and put things behind us. I just think our effort wasn't there tonight."
Andy McDonald had a goal and two assists, and Matt D'Agostini added a goal and an assist for St. Louis, which won for the third time in four nights as it scrambles to stay alive in the Western Conference playoff race.
"For us, playing back-to-back, we needed a big effort," McDonald said. "We're aware of the situation. We have injuries, younger players being called up ... it was a great overall effort."
The Canadiens did all they could to downplay the long-anticipated matchup despite facing all sorts of questions about facing Halak and dealing with Pacioretty's injury.
"I think that's more of the outside world just making a big deal out of that," center Scott Gomez said. "We knew we were going to face (Halak). He played great. He did a good job."
McDonald gave the Blues a 2-1 lead 1:06 into the second period after D'Agostini poked the puck away from Benoit Pouliot in the offensive zone. McDonald found himself alone in front of Price and snapped a wrister past his blocker.
Halpern opened the scoring by redirecting Alexandre Picard's feed into the low slot past Halak 12:30 into the opening period. Backes tied it with his 24th of the season off McDonald's faceoff win with a quick shot from the slot, beating Price at 18:59.
D'Agostini, who was also playing the Canadiens for the first time since being dealt to the Blues last March, sealed the game by converting McDonald's feed into the slot on a 2-on-1 with 1:29 remaining.
"That Halak-Price showdown, that's what everyone was talking about," D'Agostini said. "I had my opportunities in Montreal. I'm not going to say I didn't have my opportunities, but I just have found my groove hopefully here in St. Louis."
Material from team media and wire services was used in this report