Filip Kuba's tally with 1:53 remaining in 1 victory over Montreal at Scotiabank Place.
Daniel Alfredsson set up the score, carrying past a Canadiens checker in the neutral zone, then coasting up the right wing before finding Kuba on the left side. His wrister beat Carey Price to the short side to end the game.
Colin Greening tied the game in the third period for the Senators, who vaulted over idle Boston by one point (84-83) for the top spot. The Bruins take on Philadelphia at home Saturday afternoon and have the chance to reclaim the lead before Ottawa hosts the Islanders.
Ben Bishop needed to make 13 saves to earn the win.
Tomas Plekanec's first-period score was all for the Canadiens, who won the opener of this home-and-home set on Wednesday by a 3-2 count in a shootout.
Price ended with 31 stops.
Plekanec tallied at the 8:18 mark of the first period, slapping a shot past Bishop from between the circles.
Ottawa failed to click on a two-man advantage which spread from the end of the first and into the second period, and despite a 12-3 shot advantage still couldn't solve Price.
Greening finally evened the score, converting an Erik Condra rebound at 6:27 of the third period. The Sens failed to net the winner despite a power play with 4:40 left in regulation.
Despite the loss, Montreal has taken three of five games in the season series, with one final matchup scheduled for the Bell Centre on March 23...Canadiens defenseman Alexei Emelin left the game early in the second period with an apparent upper-body injury after taking the full force of a shot on his side...Habs defenseman Tomas Kaberle sat out his second straight game due to personal reasons.