The veteran defenseman snapped a 20-game goal drought on the play.
With a helper on Edmundson's tally, centreman Nick Suzuki extended his point streak to seven games.
That's the way things stood after 20 minutes. Ottawa was leading 11-10 in shots.
The Senators went ahead 2-1 at the 3:44 mark of the second period.
Left all alone in the slot, winger Brady Tkachuk buried a feed from centreman Josh Norris for his 17th goal of the season.
The Senators doubled their advantage with eight seconds left in the frame.
Left-winger Nick Paul tipped a point shot from defenseman Erik Brannstrom for his fifth goal of the season.