The GreenJackets lost 4-0 to the Charleston RiverDogs and Wheeler, who lasted just one-third of an inning in his season-opening debut a week ago, pitched into the fourth before giving up three earned runs on three walks and three hits.
"Definitely still not up to my standards," Wheeler said. "But it felt good to go out there after a bad outing and get some outs."
Wheeler initially appeared to shake off the first start that saw him surrender three earned runs in just six batters faced. He responded in his first home start of the season by striking out five of the first seven batters Saturday night.
But the 19-year-old right-hander got rattled in the third inning when he gave up a two-out single, then back-to-back doubles to surrender the first two runs of the game.
"I was leaving everything up," Wheeler said. "I had it early, but I lost it in the third inning."
Wheeler was pulled after walking the first three batters to start the fourth inning.
GreenJackets manager Dave Machemer said Wheeler's effort was a marked improvement from his start a week ago.
"He threw much better tonight. We got a lot of improvement out of him," Machemer said. "He's a young kid and he's not polished yet by any means, and as long as he gets better every time out he'll be fine."
Wheeler (0-2) got no support in the loss. Charleston starter Kelvin Perez (1-0) held the GreenJackets to two hits over seven shutout innings. He struck out a career-high nine and walked one.
"We've got to get better with the bats," Machemer said. "We're striking out too much, taking too many called third strikes. At this level, you've got to be able to make adjustments at the plate, and we didn't do that tonight."
The GreenJackets (7-3) still held on to sole possession of first place in the South Atlantic League's Southern Division standings.