Arizona acquired Hernandez from the Baltimore Orioles along with another right-handed reliever, Kameron Mickolio, in exchange for corner infielder Mark Reynolds. While Reynolds has struggled with the Orioles over the past two seasons, Hernandez has shined with the Diamondbacks in his role of setup man for veteran closer J.J. Putz.
After posting an ERA and WHIP of 4.31 and 1.437 over his 41 appearances, including eight starts, with the Orioles in 2010, Hernandez maintained an ERA and WHIP of 3.38 and 1.139 over his 74 appearances out of the Diamondbacks ‘pen in 2011. Over that span of 69 1/3 innings, Hernandez maintained 10.0 SO/9 and 3.9 BB/9.
Hernandez has improved on these marks this season with the Diamondbacks, as he currently holds an ERA and WHIP of 2.90 and 1.097 with 13/1 SO/9 and 3.5 BB/9.