5th place: Fail Mary
This was a huge play that directly resulted in a win against a major NFC competitor. The reason I don't have this play higher is because it ultimately had no impact on our playoff seeding, and it actually helped SF earn a bye. It was also a very ugly win, whereas the Pats and Chicago wins were downright inspirational. It added fuel to the fire for the haters all season. So I have it down the list a bit, but it's clearly top five.
4th place: Rice TD vs. Pats
Up until the final weeks of the 2012 season, the Patriots were the NFL's best team, both in terms of media perception and their scores by advanced stat sites like Football Outsiders. Seattle was still a struggling young team, and Wilson was still experiencing growing pains. Seattle overcame a two score deficit in the 4th quarter to shock the Patriots. Before Chicago, this was the game that officially put Wilson on the map nationally. Rice's inexplicable deep reception keyed the win.
3rd place: Tate TD vs. Chicago
With just 32 seconds left and only 1 timeout, Wilson made a questionable decision throwing a short pass to Tate near the harshmark heading away from the sideline. Nine times out of ten, the receiver gets tackled around the 6 yard line in bounds and forces the team to use it's final timeout, a sack away from a bitter defeat. Instead, Tate made one of the most impressive YAC efforts of the entire season, juking half the bears defense to just barely reach the endzone for the go ahead touchdown that helped Seattle pull out a momentum seizing win.
I have this one ahead of Rice's TD both later in the same game and in the Pats game because the degree of difficulty was so high. It was one of the most amazing efforts of the season and it happened at an amazing moment. That TD was all on Tate. The number of WRs in the NFL that could have made that play could probably be counted on one hand (Harvin being one of them).
2nd place: Lynch TD vs. Falcons with 31 seconds left
If Seattle holds on for just 25 seconds at Atlanta, they would not only have won, but they would have completed the largest 4th quarter road playoff comeback in NFL history. If Seattle had gone on to win the Superbowl, think about how this play would have been regarded then. Granted, the TD itself was pretty routine, but I think it's worthy of being this high because it was the play that completed what should have been an historic comeback.
1st place: Lynch Fumble recovery vs. Washington
I remember when this play happened and seemingly everyone said "that play WAS our season." Down 14-3, Wilson fumbled a read option keeper with most of the players around him wearing the wrong colors. If a Redskin had recovered it, it would have likely been returned for a touchdown and Seattle would trail 21-3. Instead, Lynch had the presence of mind to check on his QB, scoop up the ball, and stun everyone by running for a 20 yard gain. Seattle would score a TD later in that same drive meaning that this one play had a potential 14 point swing in a game Seattle won by 10 points. In the playoffs. On the road.
If Seattle loses that first game in Washington after falling behind 21-3, think about how different the story of this team would be right now. They'd still be the team that chokes, that cannot win a playoff game on the road, etc. We'd have lost to a hobbled RG3, which would have cemented his status as superior to Wilson, at least in the short term.
Maybe Seattle wins without that play, but emotionally that felt like the biggest play of the season for me. It was simply a huge play in an extremely high leverage situation, in the playoffs. I'd probably list it among the most critical Seahawks plays ever that didn't result in a touchdown itself.