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02/21/2013 8:46 PM ET

Right-hander Peralta opening D-backs' eyes

SCOTTSDALE, Ariz. -- When they selected Starling Peralta from the Cubs in the Rule 5 Draft in December, the D-backs knew they were getting a pretty good pitcher.

After watching him throw a couple of live batting-practice sessions, the right-hander might be better than they thought.

"I've seen him throw live twice and his breaking ball is a lot better than our reports were," D-backs GM Kevin Towers said. "I knew he had a good change, live arm, good fastball, but I've seen a better breaking ball. It's a little bit of a slurve, but he looks to command it fairly well. Deception with his delivery, a lot of arms and legs -- I don't think right-handed hitters will be very comfortable in there facing him."

Peralta needs to improve his command, and he has an uphill battle to win a spot on the pitching staff. The D-backs' rotation is virtually set with the fifth spot to come down to Tyler Skaggs, Patrick Corbin and Randall Delgado.

The bullpen appears set with J.J. Putz, David Hernandez, Heath Bell, Brad Ziegler, Matt Reynolds, Tony Sipp and Josh Collmenter.

The D-backs paid the Cubs $50,000 to select Peralta and he must be kept in the big leagues for the entire 2013 season or be offered back to the Cubs for $25,000. It is also possible that the D-backs could wind up working out a trade.

"It's the kind of arm you'd like to keep in your system," Towers said.

D-backs manager Kirk Gibson will keep a close eye on Peralta over the next five weeks.

"He's overpowering," Gibson said. "Interesting guy to watch throw this spring, for sure. Just from watching him, it looks like he's got to command the zone more. He's got electric stuff."

McCarthy working on getting feel for changeup

SCOTTSDALE, Ariz. -- Brandon McCarthy felt right at home Thursday pitching on the practice fields of the Oakland A's.

The D-backs right-hander, who spent the past two years pitching for the A's before signing with Arizona in the offseason, threw his second live batting-practice session of the spring.

The D-backs were forced to use the A's practice fields due to the snow that covered their Salt River Fields practice fields.

"I felt good," McCarthy said. "It was just trying to get refreshed after the other day, kind of start ramping up workload. I threw terrible in the bullpen and then once I got out there, I was hitting spots again and remembering what I was doing."

McCarthy's changeup is still a work in progress. He is working on getting more consistent with the pitch since adjusting his grip on it.

"Some good, some bad," he said of the changeups he threw Thursday. "That's kind of the way that journey's going to go until I can get into games and you're actually throwing it in counts that mean something. I'm starting to get a better feel for it and an idea of what I want to do with it. It's just going to be putting all that together in these next five weeks."

Steve Gilbert is a reporter for MLB.com. Follow him on Twitter @SteveGilbertMLB. This story was not subject to the approval of Major League Baseball or its clubs.