ST. LOUIS -- Wily Mo Pena made his first start in left field for the D-backs on Sunday in the series finale against the Cardinals.

Pena had started nine games this season, all as the designated hitter during Interleague Play. Pena has been working extensively on his defense over the past week, shagging fly balls and throwing to bases.

He has done enough to convince manager Kirk Gibson that he won't be a liability in the field.

"He's been working out there every day," Gibson said on Sunday. "He's had a lot of good days."

Pena burst on to the big league scene once again this season, belting five home runs in his first 39 at-bats, including a homer in his first game with the club, on June 21. He's been all-or-nothing at the plate, though, hitting .190 but slugging at a .548 clip. He has eight hits, including those five home runs.

Pena has done well as a pinch-hitter, going 3-for-7 in those situations with a pair of homers. In his second game at Chase Field, on June 28, Pena blasted a walk-off, pinch-hit homer to beat the Indians.

Putz throws from a mound with no problems

ST. LOUIS -- J.J. Putz threw a bullpen session before Sunday's series finale against the Cardinals and reported no issues with his injured right elbow.

Putz, who was placed on the 15-day disabled list on July 1 with tendinitis in the elbow, threw off a mound for the first time since receiving a cortisone injection on June 29.

"We'll see how he feels tomorrow, that's the big issue," said manager Kirk Gibson on Sunday. "He looked fine, but how does he come out of it?"

Putz began the week playing catch, then threw from just short of the pitching rubber before moving on to the mound on Sunday as he continues to build up his arm strength. The right-hander is eligible to come off the DL on July 16, but Gibson said that it generally takes pitchers 20 days to complete their full cycle of treatment.

"So far everything he's done, he's been fine," Gibson said. "Nothing alarming at all."

David Hernandez has filled in for Putz as the closer, and has converted five saves in five chances in July. Hernandez, though, will slide back into the setup role when Putz returns despite his success closing games.

"[Hernandez has] done a great job, but he's also done a pretty good job in the eighth inning," Gibson said. "But it's great for his experience. On those days when J.J. is not available, he gives us more depth in that position. Maybe his time [will come when he can] move into that spot."

Hernandez has converted seven saves in nine chances this season. Putz has 21 saves in 25 opportunities. But Hernandez won't mind returning to the setup role once Putz, the D-backs' most established closer, comes back.

"If we both keep pitching well, that means we're winning games. That's really all that matters," Hernandez said.