The Yankees swept a double header, clinching no worse than a wild-card berth with a win in the first game and then wrapping up the division crown in the second contest. Tampa Bay dropped into a tie with the Los Angeles Angels for second place in the American League wild-card race, 2 1/2 games behind Boston.
The division title for the Yankees is their second in the last five seasons after New York had won the AL East crown every year from 1998 through 2006.
New York had a 2-0 lead through four innings in the second contest before Tampa Bay tied it on homers by Kelly Shoppach in the fifth and Sean Rodriguez in the seventh.
Nick Swisher reached on a one-out double in the eighth and Mark Teixeira drew a four-pitch walk with two away. Robinson Cano, who hit a solo homer in the second inning, was walked intentionally to load the bases and that brought up Posada as a pinch hitter.
He hit an 0-1 offering from reliever Brandon Gomes into right, scoring two runs and sending the Yankees to the division crown.
CC Sabathia gave up two runs on seven hits over 7 1/3 innings, but the win went to David Robertson (4-0). He retired the last two men in the eighth and Rafael Soriano worked around a two-out single in the ninth to record his second save.
Jake McGee (3-2) took the loss by putting the go-ahead run on base in the eighth.