In the playoffs, they're all big. However, tonight's game, which looks like it will be played, could could swing this series one way or another.
First of all, the obvious. The Angels don't want to go two down in the series. I don't know what the exact statistic is but I do know that most teams don't win a best of seven series after losing the first two games. I know their are exceptions but the bottomline is that down 2-0 in a seven game series is a very uncomfortable positions to be. On the other hand, I don't think their's a single Angels fan who'd be unhappy with the series tied up 1-1 with three games coming up on the West Coast. Their's a lot of pressure on the Angels to win this game and take this thing back to Anaheim.
Then there's the pitching matchup. Of all the probable pitching matchups, this would seem to be the most lopsided one. Its also really the only one in which one guy seems to have a clear edge over the other. No matter how hot Saunders finished the year, he's just not of the same caliber of pitcher as A.J. Burnett. Burnett is a big, strikeout pitcher, the kind that you look for to start postseason games. Saunders is much more of a finesse guy and the Yankees could clobber him. Anything can happen in October, however, if their's anything the Yankees should be able to count on, it should be that A.J. Burnett will outpitch Joe Saunders at home in Yankee Stadium.
If the Yankees win they just need to go 2-3 for the rest of the series. They'll have C.C. going in two more games and they'll get to tee off of Joe Saunders one more time. Not to mention two more games at home and their other advantages over the Angels.
In the end every game counts the same, however, the momentum of the series could swing on this game.