I think the key play was either :
1) When the ref threw a key block on Rocky Bernard to spring Parker for that 75 yard TD. I don't know how that was missed, but the ref clearly tripped him as Parker went by, allowing the play to develop.
2) When the ref grabbed Marquand Manuel's leg, allowing Ward to get open at the goal line on 3rd and 28, setting up the first TD.
3) When the ref shot the Seattle CB in the eye with a pea shooter on the gadget play, allowing Ward to get open deep to receive El's pass.
4) The ref putting olive oil on Jeremy Stevens' hands.
5) The ref ordering the "wind machine" to be turned on for both of Brown's F attempts, blowing both kicks wide.
6) The ref distracting Peter Warrick on his punt return, causing the ball to drop in front of him and roll to the 2.
7) The ref giving steroids to Tom Rouen, making him boot every punt into the end zone.
8) The ref using a voodoo doll to force Hasselbeck to throw a terrible INT to Ike Taylor with a 4-point deficit.
9) The ref continually getting a hand in there to tip passes away, leading to Seattle's 5-for-17 conversion rate on 3rd down.
10) The ref throwing key block after key block inside 5:00 to play, allowing Pittsburgh to force Seattle into burning all its timeouts, and not leaving them enough time left to score twice.
11) The ref using telekinesis to force Holmgren and Hasselbeck to butcher the clock management phase of the game in both the second and fourth quarters.
12) The ref using a hip-check to keep Stevens in bounds on the second to last play, thus nullifying any chance the Seahawks had to pull off a miracle.
Probably one of those.