Crosby, who assisted on Martin's goal, then netted his 11th on a power play with 29 seconds remaining in the second period.
James Neal made it 4-0 with a goal 7:16 into the third.
At Ottawa, Ontario, Mikko Koivu scored the tiebreaking goal in the closing minutes of the third period and added two assists to lift the Minnesota Wild over the Senators 4-3..
Koivu netted the winner with 2:57 left, allowing the Wild to rebound from a 6-2 loss in Montreal on Tuesday.
Former Senators forward Dany Heatley had a goal and an assist for the Wild (14-5-4), as did Jonas Brodin. Jason Pominville had the other goal, and Zach Parise had two assists.
Milan Michalek scored on the power play as the teams approached the midway point of the third period to pull the Senators even with the Wild. It appeared that goal would at least get the Senators to overtime.
Kyle Turris and Mika Zibanejad also scored for the Senators (8-10-4), who have lost three straight and four of five.
The Columbus Blue Jackets beat the Calgary Flames 2-1 after defenseman Nikita Nikitin scored his first goal of the season 2:25 into overtime.
When David Savard's shot was blocked by Mikael Backlund in front, the puck caromed out to Nikitin, who had an empty net with Reto Berra down and out.
Nick Foligno also scored for Columbus.
Joe Colborne scored for Calgary, which has lost six straight at home.