PHILADELPHIA -- It was difficult for Zach Jackson to keep himself composed as he made that long jog out from the A’s bullpen at Citizens Bank Park on Saturday. Not only was he taking the mound for his Major League debut, he was doing so in front of a notoriously raucous crowd.

Entering the game to begin the bottom of the eighth inning of the A’s 4-2 loss to the Phillies, Jackson was immediately greeted to a chorus of boos from the majority of the 41,622 fans in attendance.

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“It was everything I hoped it would be,” Jackson said. “You don’t play in stadiums like that [in the Minors]. The crowd here has obviously been incredible. For a place to open up and make your debut, I don’t know if there’s a lot better. It was definitely cool to look out and see how many people were there.”

Jackson’s nerves were clear from the jump. He led off his first big league appearance by issuing a walk to Rhys Hoskins, which quickly prompted a mound visit from A’s pitching coach Scott Emerson. Using the break from the action to regroup, the right-hander soon locked in for a scoreless inning that kept the A’s within striking distance. He induced a ground-ball double play from Jean Segura in the next at-bat and finished off the outing with a swinging strikeout of Didi Gregorious on an impressive sweeping pitch across the outer part of the zone. It registered as a slider on Statcast but was actually a curveball, according to Jackson.

“My body was definitely just to the point where I couldn’t feel it almost,” Jackson said. “Situationally, we still had a chance to get back in that game, so I knew it was critical that I get out of it without giving up any runs. It was important to get ahead in the count. Honestly, I didn’t have much offspeed. Once I got out there, I think I was moving a little too fast.”

The only person in the ballpark who perhaps felt more anxiety than Jackson was his father, Kevin, who was part of the small group that made the trek from Oklahoma to watch him pitch. Also included in the party was Jackson’s mother, Gina, his sister, Chelsea, and his fiancé, Alex.

Throughout the outing, All four members of Jackson’s family were shown on the NBC Sports California broadcast, noticeably tightening up with each pitch and erupting upon watching the strikeout to end the frame. That strikeout pitch and Jackson’s first Major League pitch to Hoskins were both retrieved by the A’s. The baseballs will be gifted to his father, Jackson said.

“They’ve been on this journey as long as I have, especially my Dad,” Jackson said. “I’m sure he was just the same if not more worried than I was out there. So I’m glad it went well.”

That journey was not an easy one. Originally a third-round Draft pick by the Blue Jays in 2016, Jackson pitched solely in the Minors for the organization before getting picked up by the A’s in the Minor League phase of the 2020 Rule 5 Draft. He was off to a strong start at Double-A Midland in 2021, leading to a promotion to Triple-A Las Vegas. But a hip issue eventually required surgery and cut his season short. Still, his combined 2.57 ERA with 47 strikeouts over 28 innings at the two stops impressed the A’s enough to invite him to big league camp this spring.

Now that the first-game jitters are out of the way, the A’s expect to get a better look at Jackson’s impressive arsenal, which also features a changeup to go along with a curveball that Emerson compared to the one thrown by Hall of Famer Bert Blyleven.

“I’m proud of the kid going out there in this environment,” said A’s manager Mark Kotsay. “I think he showed us today that he can pitch here, and we’ll continue to look forward to good things from him.”

Saturday’s effort from Jackson was part of an all-around promising performance by the bullpen. Dany Jiménez, who entered in relief of starter Cole Irvin with one out in the sixth, finished the inning with two quick outs. Left-hander A.J. Puk, Oakland’s No. 15 prospect, followed in the seventh with a strong scoreless outing that saw him sit 96-97 mph with his fastball and record strikeouts of J.T. Realmuto and Nick Castellanos.

The trio of Jackson, Jiménez and Puk are names Kotsay mentioned during Spring Training as his likely options in the late innings when facing high-leverage spots to set the bridge to closer Lou Trivino. For their first look in the 2022 season, all three showed capable of performing in such situations.