I think David Kampf is a very important player for the Leafs.
I only watched the first period of the game last night due to the late hour. I don't know how they played after the first intermission, but it looks like they had everything sorted out.
After Kampf went down, they had trouble clearing the zone until the intermission.
I think the Leafs recent success is due in large part to having a reliable third line that can take defensive-zone face-offs, and fairly effectively clear the zone and establish the play in the other end of the ice. Without that, they tend to fumble around in their own end, creating scoring opportunities for the other team that doesn't really help them.
I also noticed that Kase and Kampf, and a random left-winger, often come on after a dry power-play to settle things down in the right end of the ice.
They sort of keep the ship steady and set things up for the top two lines.