Three of the four Red Sox losses to the Rangers came during a series sweep, in Arlington, at the beginning of May. The Red Sox are not the same team that they were from May 3-5th, and neither are the Rangers, not to mention the fact that the Sox have now earned home field advantage through the playoffs.
Meanwhile, the Rays have faced the Sox nineteen times this year, and while they haven't seemed to figure Boston out, they're much more familiar with the Sox's playing style.
In the end, it might not matter. Whoever wins tonight's one -game playoff will then have to play yet another one-game playoff against the streaking Cleveland Indians, winners of their last ten games in a row. Tito's team will get the advantage of taking on whoever survives the one-and-done play-in to the Wild Card round, and all the pitcher attrition that will entail.
Meanwhile, the Red Sox get to relax until Friday, making roster decisions and growing out those beards, while the competition fights to get to that point.
Not that there's really much danger of this team taking the first round (or any round) of the playoffs for granted, but it goes without saying that a best of five series can be dangerous. If the last few years have taught Red Sox fans anything, it's that playoff appearances aren't to be taken lightly - they don't come around every year.