Celtics are more like a 47-50 win team than a Championship caliber side when they are without Rajon Rondo + Perk and Jermaine.
Still, they should have more than enough talent to handle the Philadelphia 76ers. The Sixers are a pathetic team defensively in the paint + in team defense from their big men.
Jodie Meeks is also one of the weakest SGs in the league. Ray Allen has a major matchup advantage. Keep going to Ray. It'll pay dividends.
Iggy can defend Pierce + Holiday can defend Nate. Boston needs to run the majority of it's offensive actions through Shaq, Ray and Garnett instead. If they rely too heavily on Pierce and Nate, Pierce especially, their offense will be vulnerable to Phily's defensive strengths.
Ball movement is big too. Phily's big men can't make defensive rotations. One or two rotations and they are lost and you'll get an easy shot each time down the court. Can't have players killing the clock dribbling the ball (read: Nate + Paul).