Pena, who has not played in the big leagues since 2008, was crushing the ball in Reno, hitting .363 with 21 homers and 63 RBIs in 63 games for the Aces.
"He's been crushing it, hopefully it continues," D-backs manager Kirk Gibson said. "He's been swinging the bat well in Reno the whole time, lots of power. He's been hitting good pitching down there and we felt like playing the next games in the American League that it would be important to have a guy like him in our lineup."
During Interleague Play, games in AL parks utilize the designated hitter. Given his defensive shortcomings in the outfield, Pena is perfectly suited for the DH role and the D-backs had no other logical candidate.
Power has never been an issue for Pena, but making contact has. That seems to have changed this year, at least at the Triple-A level.
"My first time in my career I was thinking about it, wow, .363, that's a lot to hit," he said. "I worked hard in the off-season and I showed up in spring training and worked hard and I went down and tried to do the same thing."
The rise in average coincides with his emphasis on not striking out as much.
"It's different," he said. "My approach is just to hit for average. I think everybody knows that I would just worry about hitting home runs, just think about that. But I've realized I have to go to the plate and just make contact. I know I've got power. I just told myself that I have to prove that I can hit for average, too. I'm taking pitches, taking some walks and striking out less. I was surprised when I saw my numbers. I was like, wow, that's not me, not the way I used to strike out before. My main thing is just to make contact. If I make contact, something will happen. Just trying to put the ball in play and we'll see."
The club designated infielder Sean Burroughs for assignment to make room for Pena.