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The 25-year-old Lewis went a combined 3-1 with a 1.62 ERA in 17 appearances last season with Class A Lexington and Class A Wilmington. He also started three games on a rookie league rehab assignment.
Lewis missed all of the 2015 season after undergoing Tommy John surgery.
O'Brien was acquired by the D-backs from the Yankees prior to the 2014 non-waiver Trade Deadline in exchange for third baseman Martin Prado.
At the time, O'Brien was a catcher, but after experiencing throwing issues during Spring Training in 2015 he was moved to the outfield. While he put up monster numbers for Triple-A Reno, including slugging 24 home runs in 434 plate appearances there last season, he was unable to translate that into big league success.
Given a two-week stretch of everyday playing time last June, O'Brien hit .146 during that time with 19 strikeouts in 50 plate appearances. Overall, he hit .141 with five home runs in 67 plate appearances with Arizona.
Steve Gilbert has covered the D-backs for MLB.com since 2001. Follow him on Twitter @SteveGilbertMLB. This story was not subject to the approval of Major League Baseball or its clubs.