Alfredsson led an offensive charge in which 11 different Ottawa players recorded at least a point before a sold-out crowd of 20,038 at Scotiabank Place, which included several thousand Canadiens supporters who endured a long afternoon.
By the time this one was done, one large group of them sported paper bags on their heads in addition to their red, white and blue shirts.
The Senators (26-19-2) scored four times in the first period and eventually chased Canadiens starting goaltender Cristobal Huet from the game as they coasted to their fourth straight victory and fifth win in the past six contests. They halted the Canadiens' win streak at two games.
Chris Kelly had a goal and three assists and Dany Heatley celebrated being added to the Eastern Conference roster for next week's all-star contest at Dallas with a goal and two assists.
Patrick Eaves and Mike Comrie each tallied once and set up another and Wade Redden, Antoine Vermette and Andrej Meszaros rounded out the scoring for Ottawa. Ray Emery stopped 37 shots to earn the victory in goal.
Heatley will be joined at the all-star game by Montreal's Sheldon Souray, who was voted a starter on defence by the fans, and Huet, who was also added Saturday - the only highlight of rough day for him.
Huet lasted less than half of the game, giving up six goals on 25 shots before being replaced by David Aebischer. Aebsicher made seven stops the rest of the way.
Souray had a power-play goal to set a franchise record for power-play markers in a season with 12, eclipsing a mark shared by Guy Lapointe, Matthew Schneider and Patrice Brisebois.
Christopher Higgins and Craig Rivet had the other goals for the Canadiens (25-15-5).
Montreal had a 12-point lead in the standings over Ottawa on Dec. 23. But with a 9-1-1 record in their past 11 contests, the Senators have closed to a point in the hunt for second place in the Northeast Division.
The Canadiens have now lost four of their past six games, six of nine contests, and are 4-7 in that same 11-game span. Montreal completes its three-game road trip Monday night against the Detroit Red Wings.
The afternoon start was the first game of CBC's Hockey Day in Canada tripleheader and it was Montreal which applied the early pressure, forcing Emery to make a series of saves.
However, Redden snapped a shot over Huet's shoulder 4½ minutes in and that changed the momentum. Ottawa went on to fire a season-high 20 shots at the Montreal net in the first and, after Vermette made it 2-0 midway through, Comrie and Alfredsson scored power-play goals little more than two minutes apart to send the Senators to their dressing room with a 4-0 advantage.
With Montreal shorthanded early in the second, Higgins missed an open net on a 2-on-1 break and the Senators came right back down the ice and made it 5-0 on Heatley's rebound goal.
After Kelly made it 6-0 at 3:31, Huet was gone and the Canadiens responded with goals just 22 seconds apart, but the Senators scored twice more before the period was over.
Souray made it 8-3 with his power-play marker in the third.
The Canadiens went 1-for-6 with the man advantage; the Senators finished 3-for-5.
Notes: Eaves and Meszaros were named to play in the NHL YoungStars Game on Saturday. . . Ottawa defenceman Anton Volchenkov returned after missing Thursday's game with an ankle injury, but the Senators were still without centres Mike Fisher and Jason Spezza. . . Centres Steve Begin (back spasms) and Radek Bonk (neck) and defenceman Janne Niinimaa (flu) all sat out for Montreal, as did right-winger Aaron Downey, who was a healthy scratch. . . Ottawa plays host to Washington on Tuesday.