Despite being stricken with cerebral palsy, an incurable brain disorder that affects muscle movement and coordination, the excited 2-year-old threw out the first pitch at Miller Park before Wednesday night's game.
Watch Mack's pitch here.
Then, in the sixth inning, his dad lined a pinch-hit, go-ahead home run for the Brewers, who beat the Nationals, 7-5.
What a combination. Mack with the pitch, Casey at the bat.
Mack was able to see his dad's homer in person before heading home with his mom. They phoned Casey after the game to congratulate him.
"Good hit, daddy!" Mack said, according to MLB.com.
"That was about as good a 'congratulations' as I could get," Casey said. "You can't help but smile when you see him. He makes the bad days a little easier and the good days that much better. You just can't help smiling when you see how he reacts. As young as he is, he gets it a little bit."
Mack's appearance was part of an initiative by Brewers wives to raise money and awareness for United Cerebral Palsy. Casey, whom the Brewers claimed off waivers, is a having a strong season at the plate while getting his first opportunity to play regularly in the majors.
"As a father, that's going to me a moment I remember for a long time," Casey said. "He's something special. To go through what he's going through and to keep on plugging, no one even notices he has anything wrong with him most of the time.
"He's been a big inspiration to me. The way some of the guys have taken to him is really special. If you would have asked me a few years ago if I would even be on a big league field, let alone be able to share it with my son in any way, shape or form, I was pretty lucky to have that happen."