ATLANTA — Nobody expected Ranger Suárez to keep pitching as well as he did last season.

That’s neither a criticism of the Phillies left-hander nor an indictment of him as some sort of one-year wonder. It’s merely an acknowledgment of just how dreamy — and historic — his 2021 really was. With a 1.36 ERA in 106 innings, Suárez became the first pitcher since Bob Gibson — Bob Gibson! — in 1968 to post a sub-1.50 ERA in at least 100 innings while making a minimum of 10 starts.

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When that is your starting point, regression is all but inevitable.

But the Phillies also didn’t plan on quite this much slippage. In nine starts, including Wednesday night’s clunker against the Atlanta Braves, Suárez has a 4.74 ERA. He has completed seven innings only once and allowed as many walks (19) and home runs (six) in 43⅔ innings as he did all of last season.

“He’s just off,” manager Joe Girardi said.

Figuring out the cause of Suárez’s struggles and getting him back on track is the immediate concern. The Phillies have good reason to be bullish about their starting pitching, especially with Zack Wheeler once again looking like a Cy Young Award candidate. Suárez is a big part of the equation at the back end of the rotation.

But there’s also a long-term issue that will need to be tackled. Suárez has never thrown more than 124⅓ innings in a season — and that was back in 2018. How many innings can the Phillies reasonably expect from him this year? Is 150 a realistic number? What if it’s less than that?

“There’s a lot of clubs that will add 40-50 [innings],” Girardi said of a safe year-over-year buildup of a pitcher’s workload. “I think you have to check how the pitcher’s doing. We don’t have an exact rule. I’ll tell you that right now. I think you’ve got to watch him. When you can give him a break, you try to give him a break. But he’s in our rotation, and we’re planning [for] most of the year.”

A few days ago, Girardi met with president of baseball operations Dave Dombrowski, pitching coach Caleb Cotham, and director of pitching Brian Kaplan to discuss using a sixth starter for one turn through the rotation. In that scenario, the Phillies would call up lefty Bailey Falter, who didn’t make his scheduled start Tuesday night in triple A in preparation for possibly joining the big-league club on the road this week.

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Girardi said the move to a six-man rotation would be made with more than Suárez in mind. He noted that Wheeler and Zach Eflin, in particular, may benefit from an extra day of rest after being out with COVID-19 earlier in the month.

But the Phillies could use Falter to help manage Suárez’s innings over the next few months. In a May 11 spot start in Seattle, Falter held the Mariners to one run in 4⅔ innings. He hasn’t allowed a run in 10⅓ innings over three starts in triple A.

Regardless of how the Phillies handle Suárez’s workload, they must figure out why his command has eluded him. He’s averaging 18 pitches per inning, too many to consistently get deep into games. In his last two starts, he has thrown only 99 of 172 pitches for strikes.

After issuing a season-high four walks against the Braves in a performance that Girardi described as “all over the place,” Suárez said he was unsure of the root cause. Mechanics are one possibility. Fatigue is another. Maybe it’s a combination.

“I really don’t know,” Suárez said through a team translator. “I feel fine. I can tell you that. But the control is not there.”

Suárez’s success is predicated on locating his sinker and getting ground balls. He doesn’t light up a radar gun. So while it’s notable that his average fastball velocity has trended downward over his last few starts — from 94.4 mph on May 14 in Los Angeles to 93.3 mph on May 20 against the Dodgers and 92.7 mph in Atlanta — the Phillies are largely unconcerned.

Girardi speculated that the velocity dip against the Braves stemmed from an arduous second inning in which he threw 33 pitches and gave up four runs.

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“I think his stuff is still really good,” catcher J.T. Realmuto said. “The ball is coming out of his hand fine. When he makes his pitches, he gets outs. He’s just not commanding the ball as well as he has in the past. He’s missing a lot more pitches over the plate. He’s falling behind in counts. You’re seeing him walk guys in 3-0 counts. That’s just not him. I don’t know if it’s something mechanical or what, but the command just isn’t there for him right now.”

Suárez will have until next week to figure it out. If the Phillies stay on rotation, he would start Monday in the holiday 4:05 p.m. opener against the San Francisco Giants. If Falter gets called up for a start, Suárez likely would be pushed back by one day.

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“We’ve got to find a way to get him back on track,” Girardi said. “His command has just not been the same as it was last year.”

Suárez may never be that good again. That’s fine. But the Phillies believe he can be more effective this year, for however many innings he’s able to give them.