At 11 p.m. ET on Tuesday, the 21-year-old found out he had been called up to the Majors. At noon on Wednesday, Grissom was en route to Fenway Park to make his debut. And at 9 p.m., he was flipping his bat as he watched his first big league hit soar over the Green Monster.

Starting at second and batting ninth, Grissom went 2-for-4 with a strikeout and a stolen base in his debut, securing his first career hit and homer in one at-bat and helping to turn two double plays in the Braves’ 8-4 win over the Red Sox.

Grissom reached base in his first at-bat after grounding into a forceout in the third. His next time up, he struck out on four pitches to open the fifth. When he stepped up to the plate for his third at-bat, Grissom hammered a first-pitch fastball out of the ballpark.

Grissom became the youngest player in AL/NL history to homer and swipe a bag in his debut — though watching him play, it’s easy to forget his age. Whether it be his composure on the field or the conviction in his bat flip, Grissom is already displaying a big-league attitude just one game in.

While his offense stole the show, Grissom slotted in nearly seamlessly at second despite playing just seven games at the position this season. Primarily a shortstop, Grissom will be getting reps at second with infielder Orlando Arcia (left hamstring) and Ozzie Albies (fractured left foot) sidelined. Grissom’s one blip came on a hopper from Bobby Dalbec, which the second baseman bobbled but quickly recovered to get the force out at second.

Before his debut, Grissom reached out to his parents once he learned of his callup, but Tuesday’s late-night phone call was so unexpected that the No. 98 prospect in baseball initially thought he was in trouble.

“I couldn’t even speak for a long time,” Grissom said through a smile that seemingly hasn’t waned all day. “I mean, all my childhood dreams came true. … You think you’re going to react a lot easier and a lot better, and then it happened and I thought I was having a heart attack.”

When Grissom joined the big league team at Fenway, he was greeted by Michael Harris II, who had a similar experience nearly three months ago, when he was called up from Mississippi on May 28.

“What better situation can I be in?” Grissom said of having Harris by his side. “To have one of my boys who’s already doing this and can show me the way — which is just ridiculous — I don’t think anyone’s gotten blessed as I did.”

Grissom and Harris were both taken by Atlanta in the 2019 Draft: Grissom in the 11th round, and Harris in the third. The two have made their way through the system together, making their Rookie-ball debuts in ‘19 before advancing to High-A Rome in ‘21 and then Mississippi this season.

“I think he said five different times that it’s crazy that he’s actually up here in a big league cage at a big league field, especially Fenway being his first park,” Harris said. “I’m extremely happy for him. We were drafted the same year, so we’ve been together pretty much every year, and for him to be up here with me now the same year I get up … It’s great.”

Grissom has become one of the best contact hitters in the Minors over his first two full professional seasons. The 21-year-old opened this year with High-A Rome, where he hit .312/.404/.487. That prompted a mid-July promotion to Double-A, where he slashed .363/.408/.516 over 22 games.

Across both levels, Grissom has totaled 14 home runs, 67 RBIs, and 27 stolen bases to go along with a 12.2% strikeout rate.

“I heard from the guys that power is real,” Snitker said. “And he started kind of showing up this year and he was always talked about his bat-to-ball skills, kind of the reason why they drafted him.”