OK, the Yankees hit better at home. Of course they do. But if Yankee pitching was so abysmal in the first few games of the series, moving to one of the worst pitching parks in baseball couldn't help.
While Yankees pitchers obviously suffer from their home ballpark, they don't feel the effects nearly as much as opposing pitchers. While the Yankees' OPS is 90 points higher at home, their opponent's OPS is just 27 points higher in New York.
This does translate into big-time results. The Yankees outscore their opponents by almost twice as much when at home, with a run differential per game of +1.3 in the stadium, and +.7 on the road. On the road, the Yankees are about a .500 team (43-38), whereas at home, they win about 65 percent of the time (52-29).
What does this mean? The Yankees have a huge home field advantage. They are built for their park, and while their pitchers suffer a little bit from the home run friendly stadium, their opponents suffer much more.