The all-time single season performance Mariners rotation

Oakland Athletics v Seattle Mariners
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Mariners 2003 Jamie Moyer 

One of the greatest inning-eaters in MLB history, Moyer pitched a quarter-century. His best season came in his 40-year-old campaign in Seattle, being his one All-Star Game nod of his career. 

Being one of the most underrated pitchers of all time, Moyer is a perfect fit for the rotation and his ‘03 deserves its flowers. 

In that season, he went 21-7 with a 3.27 ERA. Never the most overpowering pitcher, he worked around striking out only 5.4 batters per nine innings to limit runs. His 132 ERA+ was the best of his career over a full season, and his fifth-place finish in Cy Young Award voting was the best of his career.