Smith has already made several nice catches in left field, including a running grab near the wall in left field Sunday against the Tigers that saved a run on Nick Castellanos' line drive.
"He's done a nice job and made some really nice plays. He played in a ballpark in Colorado that was a tough outfield. He has experience," said Padres manager Bud Black.
"There's been some really nice plays, some difficult plays in terms of routes and angles. He's been on top of it."
Smith got most of his playing time as a designated hitter with the A's the past two seasons. He appeared in 66 games in the outfield in 2012 and then 58 a year ago with the A's.
"I probably took a couple steps back in Oakland since I was a DH and didn't have the opportunity to go out there a lot," Smith said. "That's one of the things I've enjoyed about playing here. I like playing defense. It keeps me in the game, keeps me athletic and keeps me [mentally] in the game."
Smith said that while he's enjoying getting the chance to play in the field more, he's not focusing any more on defense than he has in the past.
"It's kind of all-encompassing. You want to be the best you can be at all aspects of the game and not be pigeonholed," he said. "Everything you do, you want to be great at it. That's how I approach it."
With Carlos Quentin on the disabled list, Smith has made 10 starts in left field, including Monday night against the Rockies at Petco Park.