It was New York's fifth straight win.
Martinez smashed a three-run home run in the fourth while Sheffield and Hideki Matsui had three RBI each.
Posada went three for four with two RBI as part of what became the Yankees' first three-game sweep this season.
The game was tied at 9-9 when Jeter opened the fifth with a homer to right.
The win went to Paul Quantrill (1-0), who threw two scoreless innings of relief.