After a surprising start, the Habs trailed the Sens by five points in the standings. Their 3-1 loss extends that margin to seven.
After a first-period power play goal by Montreal's Andrei Markov, the Senators dominated the game. Only Cristobal Huet's play kept the score at 1-0 Montreal for much of the day.
The Senators pressed the issue late, finally managing to score two quick goals before adding an empty-netter. Chris Neil scored the game-winner, while Daniel Alfredsson scored two goals and Dany Heatley registered two assists.
With the win, the Senators give themselves breathing room at the top of the division. That's sure to be appreciated by the Ottawa players.
The Habs' next game comes on Tuesday against the Maple Leafs in Toronto.