Hamilton played left field for the first seven innings of an 8-2, 10-inning win against Nashville at First Tennessee Park. The 2010 AL MVP is 1-for-7 for a .143 batting average in his first two rehab games.
The 33-year-old Hamilton is on the 15-day disabled list after undergoing right shoulder surgery in February. He was acquired in a trade with the Los Angeles Angels on April 27, with Los Angeles expected to pay most of the remaining $80.2 million he is owed.
Hamilton hit .305 with 142 homers and 506 RBIs in five years with Texas before he signed with the Angels before the 2013 season.
Hamilton came up with a runner on first in the first inning and struck out swinging against Kendall Graveman, who began the year in Oakland's rotation. He then had three straight groundouts.
"I saw more pitches," Hamilton said. "It felt better overall, just my swing. After that first at-bat, I put good contact on that [pitch], a good swing so it was a lot better."
Defensively, Hamilton made a nice catch on Jason Pridie's long fly ball at the wall in the third.
"Defensively, I thought he looked real well," Express manager Jason Wood said. "That ball he ran down in the left-center field gap was tremendous. He got a good jump on the ball. Physically, he looks good.
"I think the offense is more of a timing issue. This is somewhat of a spring training for him so he's got to get some at-bats under his belt. His batting practice is very good so it's a matter of time before he starts getting to where he needs to be offensively."
The No. 1 overall selection in the 1999 draft has had trouble with drugs and alcohol for much of his career. He self-reported a cocaine and alcohol relapse this past winter.
Nashville shifted its defense on Hamilton, putting an extra player in shallow right field while leaving third base open.
"That's part of the game, but the last thing you want to do is think about it," Hamilton said. "The best thing you can do is go up there and hit the ball hard. They do a lot of shifting around the league now."
Hamilton obliged an unusual request before the game when a fan asked him to sign a baby's butt.
"That's happened before. ... When you play long enough you're going to see a lot of crazy stuff," he said.
Hamilton will remain with Round Rock as it begins a four-game series against Omaha in Texas on Tuesday.