"I think he was 9 years old," Machado said. "He was a little stud Little League player and I met him -- I was good friends with his dad -- and he was scared of me. [Because] I'm the varsity coach."
Fast-forward almost a decade later, and Moniak is no longer a scared little kid. After years of travel ball, after becoming just the fourth freshman at La Costa Canyon to make the varsity baseball team, after Perfect Game National, Tournament of Stars, the All-America Game and Team USA -- that little kid is nowhere to be found.
"[Moniak is] relaxed and levelheaded," Machado said of the center fielder just a week ahead of the 2016 Draft. "[He] doesn't let anything really faze him."
Moniak hasn't let any pitchers faze him during his final season at La Costa -- he hit a team-best .476 with seven home runs and three times as many triples (12) as doubles (4) -- and he also hasn't let the approaching Draft, and the speculation that comes with it, get to him either.
"I'm just a normal kid that plays baseball," he said. "[The Draft] definitely doesn't affect my life in general. It's cool to look at, it's cool to think about, but I definitely don't let it affect who I am.
"If anything, my teammates give me crap for it, just to mess with me and keep me grounded. But I'm just the normal Mickey to them."
"The normal Mickey" has a chance to be one of the top picks during this year's Draft, and the highest picked player out of La Costa's program -- which has had four players drafted straight from high school.
Moniak, who is committed to UCLA, is the No. 5 overall prospect according to MLB.com after rapidly rising up the boards thanks to his play last summer and during high school this year. His scouting report depicts a player who could wind up being a five-tool guy at the Major League level:
"Moniak makes consistent hard contact against high levels of competition. He has a good approach at the plate and can spray line drives to all fields. Moniak has more doubles power now, but there's room in his frame to add strength. His above-average speed works on both sides of the ball, and some see a future Gold Glove caliber center fielder."
Much of that ability comes from Moniak's composure inside the lines.
"I trust in what I do as a baseball player," Moniak said. "I don't try to go out there and do too much. I like to stay in the gaps, stay within my game and hit line drives all over the field. But when you go up there, and it's you vs. the pitcher, you've got to be confident."
And that confidence might stem from the fact that this is old hat in the Moniak family. His father, Matt, played college baseball at San Diego State, while his grandfather, Bill, played five years professionally under the hitting instruction of Ted Williams.
Or it might be simply that Moniak has put everything into being the best player he could possibly be, starting from when he was 2 years old in a YMCA tee-ball league, to his four years with La Costa.
"He plays in a really top program in the county, and we expect them to come out every day and work their tails off," Machado said. "That's the only way you can progress as a baseball player. He bought into it. Even with all that hype, he was the first one there, working his tail off, making the other guys better."
Wherever the confidence comes from, it's days away from paying off. While Moniak is excited about the possibility of one day playing for his hometown Padres, he's more excited to simply take the next step in a life that has always been about baseball.
"Whatever team drafts me, it'd be a dream come true to start a professional career and hopefully fulfill the bigger dream of being a Major League baseball player," he said.
At this point, the chances of that goal coming to fruition are high. After all, the scared 9-year-old kid is nowhere to be found. He hasn't been around for a while.