Alfredsson, who returned after missing four games because of a nagging hip injury, had two goals and three assists, and Heatley had a goal and three assists as the Senators' big three came together for the first time in 13 games.
"Well, clearly it's a lot of fun," Spezza said. "We enjoy playing with each other and those guys seem like they're rested up. Sometimes the injuries can be a blessing in disguise. Both guys were really good, really hungry, and we moved the puck real well."
Spezza gave the Senators' a 2-0 lead 1:42 in with a pair of goals 1:20 apart. The playmaking center assisted on goals by Alfredsson and Heatley before completing his first NHL hat trick on a power play 13:36 into the second to increase Ottawa's lead to 5-0.
"I had a good idea that I was going to have a chance to get it," Spezza said. "When you get two like I got early you feel a little bit better about your game."
Spezza assisted on Alfredsson's second of the game, on a power play 2:28 into the third, for his sixth point of the night.
Andrei Kostitsyn scored Montreal's only goal during a 5-on-3 advantage with 25 seconds remaining in the second.
Ray Emery made 33 saves to win his second straight start.
With 72 points, Ottawa opened a five-point advantage for the Eastern Conference and Northeast Division leads over Montreal, which had closed to within one following a 4-3 win over the Senators on Tuesday.
"It's great, especially playing at home here on Saturday night against Montreal," Alfredsson said. "They've been playing really well. We needed the two points to kind of pull away a little bit, so it felt really good."
Alfredsson's five points increased his season total to 73 in 49 games. Spezza has 71 points in 50 games, and Heatley, who has seven points in two games since returning from a separated shoulder, has 63 in 45.
"We're always wary of them," said Canadiens center Bryan Smolinski, a former Ottawa teammate of all three players. "I think that line has killed us every time that we've played them. You can see the team they're not when they're not in the lineup. They're an unbelievable trio.
"Alfie, I think, makes that team go and if you're not mindful of what's going on -- I've been on that team and they can bury you in the first five minutes as well as anybody."
Heatley had two goals and an assist in Thursday's 5-4 win over Florida, his first game since he injured his shoulder in Ottawa's victory over Detroit on Jan. 12.
"It felt good to be out there again, the three of us together, and I felt the team played a real solid game," Heatley said.
"They came out obviously effectively -- the first five minutes and we were down 3-0," Canadiens captain Saku Koivu said. "It's not the situation we wanted to be in, especially against a team like that."
Spezza was opportunistic in giving Ottawa a 2-0 lead. Huet stopped Heatley's shot from the left side, but the puck sat beside him in front of the goal line as he fell to the ice. Spezza outraced Smolinski and pushed the loose puck over the line for his second of the game, 22nd this season.
"The puck was following me, and it's always nice when you get a couple of early ones," Spezza said. "You always feel a little better about your game."
Alfredsson ended Huet's outing when he made it 3-0 with his 33rd goal.
"They definitely played a great game," Huet said. "We were aware of that and we wanted them to have their best players in the lineup but we didn't compete enough so it was a pretty embarrassing night for us."
Heatley scored his 28th at 10:17 of the second, batting his own rebound past Price to finish off a passing play begun by Alfredsson and Spezza.
"They're probably one of the best lines in the NHL," Price said. "Every time they're on the ice they seem to be playing offense. They're never playing defense and you've got to give them credit, they work hard and they work well together."
- Huet ended a streak of 13 consecutive starts Thursday. He was 9-3-1 over that stretch.
- Canadiens D Roman Hamrlik missed his third straight game because of a viral infection.
- RW Mathieu Dandenault was left out of Montreal's lineup as struggling RW Michael Ryder returned after sitting out three games.
- Spezza had a goal and four assists in a 7-2 win over Toronto on Oct. 26, 2006.