Don't Worry....Yet

In the 35 years from 1969 through 2004, the team with best overall winning percentage won the World Series only eight times. Let me emphasize: the team with the best regular-season record has won the World Series only 23% of the time. The winners include some of the best and best-known teams of our time: the 1970 Orioles, the Big Red Machine in 1975 and 1976, the Mets in 1986 and the 1998 Yankees.

How about the teams with the best September record? The answer is exactly the same: they won eight World Series, too. Same impact. In six of the eight examples, however, the team with the best September record was also the team with the best overall record. So there's a lot of overlap between the two groups.

In fact, in about half of the last 35 years (17, to be exact), the team with the best regular-season record was also the team with the best record in September. Of those 17 teams, six won the World Series. Even teams that were Good and had Momentum won it all only 35% of the time.
http://www.hardballtimes.com/main/article/ten-things-about-momentum-in-the-postseason/
http://www.nmia.com/~roberts/baseball/33.jpg