Craig Anderson stopped 31 shots to help hand the Red Wings their third straight loss.
Eric Gryba opened the scoring 5:46 into the game and Spezza and Ryan then added power-play goals to put the Senators ahead 3-0.
Spezza scored again in the second period, giving him seven goals for the season, and Ryan added his sixth of the campaign in the third.
The Red Wings have scored just one goal over their last eight periods of action. They did not produce a goal during the final two periods of a 5-2 loss to Phoenix on Saturday and were then shut out by San Jose on Monday.