Lucas Sims’ second career start began about as poorly as he could’ve imagined.

After quietly retiring Marlins leadoff man Miguel Rojas with a soft pop to right field, Sims fell into murderer’s row, the Marlins’ outfield: He hit Giancarlo Stanton, walked Christian Yelich and Marcell Ozuna brought them home with a three-run fly. To make matters worse, catcher J.T. Realmuto took Sims deep in the next at-bat.

“I just have to be better,” a candid Sims said.

The Braves went on to lose 4-1 on Sunday, but it wasn’t a wasted effort on Sims’ part.

The 23-year-old, known to grow more aggressive after slow starts in the minors, pitched five scoreless innings. After facing eight batters in the first, he saw 12 over the next three. He retired 11 of the next 14 he faced after the back-to-back homers.

Five Marlins reached base across Sims’ last five innings.

“I made the realization I had two options: I can either roll over and it can get ugly, or I can go out there and make the most of it and try to keep us in it,” Sims said. “Chose the latter. The first one’s not really an option.”

Braves manager Brian Snitker liked how Sims mentally handled his slow start.

“He could’ve caved in after the first but he kind of regrouped and that was good to see, that he stretched that game through six innings after the first inning he had,” Snitker said. “So that’s pretty good right there.”

Braves rookie Sims gave up four runs on two first-inning homers in 4-1 loss to the Marlins on Sunday. (Video by David O'Brien)

The home run has long plagued Sims. He’s allowed three in 12 major league innings after giving up 19 in 115 1/3 innings. Ozuna hammered a curveball, while Realmuto put a slider into the seats.

“Yeah, they both were just bad pitches,” Sims said. “I didn’t execute. They were bad pitches.”

Sims led Gwinnett in starts (19), innings (115 1/3) and strikeouts (132). The strikeouts have yet to translate: He has six in 12 innings. Sims is learning what may be a put-away pitch in Gwinnett isn’t always as generous in the majors, according to his manager.

“Everything he’s going to experience is going to do nothing but help him for his next start, and then the next start after that,” Snitker said. “It’s nothing you can replicate in Triple-A. I mean, till you get up here and face these lineups … He probably threw some pitches today that would get strikeouts or outs in Triple-A, and he didn’t (get them here) and you learn from that.”

Overall, Sims said he’s underwhelmed by his standards.

“I thought they’ve gone alright,” he said regarding his first two starts. “I just expect more out of myself. I should be better for these guys. Learn from it and move on. Prepare for the next one.”

“He’s a ballplayer,” Snitker said. “He competes and gets after it. And he’s going to be able to help himself on the mound - fielding his position, holding runners, he’ll hit once he gets some at-bats under his belt – there’s just so much to like about this young man. He’s going to go out there and learn from it and just continue to get better.”

Sims’ next scheduled start is Sunday in St. Louis. It will be his first away from SunTrust Park.

“There’s a lot of learning to be done,” he said. “You look back and see what didn’t go well, what did go well. So take the day off tomorrow (Monday) and back on the ground Tuesday.”