Luis Perdomo posted 29 times in 2017. He tied for the team lead in quality starts. More than a run was shaved off an ERA that still sat at 4.67 at the end of his second season.

This is where the conversation starts when Padres pitching coach Darren Balsley is asked about his 24-year-old right-hander. The “buts” come next.

“Could he have pitched better? Yes,” Balsley said. “Did I expect him to? Yes. But did he do some good things along the way? Absolutely.

“But he’s got to take the next step. He’s not a Rule-5 anymore.”

To be fair, Perdomo’s steps to date have been considerable while growing up on the job. He spent most of 2015 in the Midwest League, jumped all the way to the majors as a Rule 5 pick the following December and has both endured growing pains and flashed signs of even greater potential over the last two seasons. The organization’s long-term trajectory remains pointed toward 2019 and beyond, but a few more growth spurts for Perdomo would go a long way toward a patched-together rotation exceeding industry expectations this summer.

Assuming Perdomo is in, that is.

To date, Padres manager Andy Green has only committed to him having a leg up on the competition to join veteran Clayton Richard and newcomer Bryan Mitchell in the opening-day rotation and Sunday’s effort was not a step in right direction.

Perdomo walked three, surrendered a grand slam to Hunter Pence and yielded a run-scoring single to Austin Jackson in an opening inning in which he found the strike zone on just 16 of his 33 pitches for strikes. He walked another in a scoreless second and got through the third unscathed but – as seen at times in Perdomo’s career – it only takes one inning to mar an outing.

“He’s got work ahead of him,” Green said. “We pushed him so hard to be aggressive (after Tuesday’s outing) and to attack and to me it was quick today. His translating attack is go faster, which isn’t the same thing. Sometimes you get a young guy and they hear attack … and sometimes it just goes quick. That’s what it looked like today. He was just quick. He did a better job as the game went on of slowing down, but I think overall he was just quick today.”

Perdomo showed much better in Surprise while striking out five Royals on Tuesday, but also allowed a run in his second and third innings of work after looking sharp to start the game. On Sunday, Perdomo said, he was cutting off his sinker in a wild first inning.

“I need to be locked down on every hitter I’m going to face,” Perdomo said Sunday through an interpreter. “… Sometimes I try to do too much with a hitter instead of trusting my stuff and just going with what I know and the scouting report.”

Added Balsley: “He knows we expect that. Usually what we ask him to do he does. He’s trying. He’s competing. It’s a reality of every-pitch-matters-type deal.”

Perdomo’s stuff works, too.

Among qualifying starters in 2017, only Blue Jays ace Marcus Stroman’s 62.1 percent groundball rate topped Perdomo (61.8). Yet opponents’ batting average (.260) and on-base-plus-slugging (.549) on groundballs sat noticeably higher than the league averages (.245 and .512), suggesting that improved infield defense could immediately supply a boost for a pitcher who already shaved his hit and home run rates from 11.5 and 1.4 per nine innings to 10.0 and 0.9, respectively, from Year 1 to Year 2 in the majors.

Enter Freddy Galvis at shortstop, where the Padres ranked last in the majors in defensive runs saved throughout Perdomo’s stay in San Diego. That’s one reason his confidence won’t be lacking.

“I just have to make sure I execute my pitches,” Perdomo said. “I don’t have to worry about Galvis making the plays back there. I’m glad to have him back there.”

Most things, of course, remain up to Perdomo.

Like the consistency of an attack that waned at times last year and in his first Cactus League appearance earlier this week.

There’s also more punchout in his game – just 6.5 per nine innings to date – if he can commit to living on both sides of the plate with intent.

“I think it’s just being able to use his fastball, his two-seamer, to both sides,” Padres catcher Austin Hedges said. “He’s really good arm side. I think if he’s capable of doing that glove side, to both lefties and righties, so guys can’t look in one general area. It’s so dominant on the arm side. At the same time, when a guy has seen it over and over and over, they know how to make adjustments.”

Now it’s Perdomo’s time to make adjustments.

To throw more strikes (his walk rate jumped from 2.8 per nine innings in 2016 to 3.6).

To, generally, progress.

“For me, he’s young and still learning,” Green said. “He’s got two years in the big leagues now. He’s still a very young pitcher. Today, I’d rather see that side of the mistake over taking a few pitches off. He’ll learn and grow from that.”

Green added: “We’re definitely pushing him to make big strides.”

Perdomo is pushing himself, too.

“I agree; it’s my third year,” he said. “I think this is the year where I’m going to do something great.”

[email protected]; Twitter: @sdutSanders