All Red Sox/Yankees games are crucial.
More of a statement series than anything but if the Yankees sweep, we're looking at a very different AL East that will be more than entertaining the rest of the way for sure. Crucial? I think there are plenty of Red Sox fans that feel they have to take two of three, not only to keep distance but as a late season statement that can linger into the post season.
The Yankees don't like the wild card. Di Maggio, Gehrig, Ruth, Reggie, and others, would be ashamed to take a Wild Card behind the Red Sox. Sure, they'll take it but I think they smell the top of the East and want it...badly.