AUGUSTA, Ga. — The kid took his old man’s advice.

It was as beautiful as it was moving.

Don’t wait to do something.

Sam Bennett didn’t.

Playing in his first Masters as the 23-year-old reigning U.S. Amateur champion — having captured that prestigious title last summer at Ridgewood Country Club in Paramus, N.J. — Bennett shot a bogey-free 4-under 68 and stands just three shots out of the first-round lead.

This is what made the day truly magical: Sam’s late father, Mark Bennett, was surely watching the proceedings from high above the cathedral of Georgia pines.

Mark Bennett, after an eight-year battle with early-onset Alzheimer’s that took over his mind and body at age 45, finally succumbed in 2021. About a year before he died, in a quiet moment at the family’s home in Madisonville, Texas, Mark Bennett slowly spoke these words to his son: “Don’t wait to do something.’’

Sam asked his father if he could write those poignant words down on a piece of paper for him. Mark Bennett struggled as he scrawled them down with a pencil, signing it, “Pops.’’

Those were the last words Mark Bennett ever wrote.

Sam put the piece of paper in his truck as a keepsake and later went to a tattoo parlor and had the ink forever emblazoned on his left forearm.

Don’t wait to do something.

Sam Bennett did some rather remarkable things with that left forearm and the rest of his body and mind on Thursday around Augusta National. He birdied the first hole, one of the trickiest holes on the course. Then he chipped in for eagle on the par-5 second hole and was 3-under through two holes.

He didn’t wait to do something.

“I couldn’t have dreamed of a better start,’’ Bennett said.

Bennett made the turn in 4-under, tying the tournament record for the lowest first nine by an amateur.

No amateur, it should be noted, has ever won a Masters. Don’t rule that out here given Bennett’s story of resolve and the powerful presence his father still has in his life.

“Oh God, Sam would give anything for him to be here right now,’’ Bennett’s mother, Stacy, told The Post, still beaming after her son’s round. “He’s so young. He’s just a gentle giant. He just exudes a whole lot of confidence. He’s always been like that, but not cocky. Calm and confident. His dad was like that. He’s got the mannerisms of his dad.’’

Stacy and Mark Bennett attended the 2018 Masters as fans, three years before his death.

“I had to really keep him close,’’ Stacy recalled, “because that’s when he started to really go downhill.’’

Bennett’s college coach from Texas A&M, Brian Kortan, is caddying for him this week and is the perfect person to walk alongside of him because of a powerful symmetry they share.

Kortan’s father died of cancer when he was young. The two, according to Kortan, have talked about that for countless hours since Bennett began playing for him.

“We’ve got some parallels in life,’’ Kortan told The Post Thursday. “It’s more than just talk. I’ve lived it as well. To watch the person that was there every step of the way for you and all of a sudden, he’s not there, it’s hard. And it was hard for Sam. Hard for the whole family.’’

Thursday wasn’t hard. Bennett made it look easy. When faced when possibly closing his round with a bogey, staring at a nervy 4-foot par-save putt on the 18th with playing partners Scottie Scheffler, the No. 1 player in the world, and Max Homa watching, Bennett calmed buried the putt to preserve his blemish-free card.

“There’s very few things that I like more than playing a round of golf bogey-free,’’ Bennett said afterward. “That’s where I want to be, to be able to hit those shots with the crowds and the pressure. I loved it. I’m experienced. I feel like I’m ready for this stage. When the pressure is on, I tend to play pretty well.’’

Bennett relished the final two holes, saying, “It was cool walking up 17 and 18. It was kind of gloomy all day, and then on 17 it was probably the prettiest view looking up that fairway, and 18 as well through the chute, the sun was shining.’’

Mark Bennett was watching, and surely smiling.

“He’s always with me,’’ Bennett said.

“A bogey-free 68 at Augusta? Man, does it get better than that?’’ Kortan said. “He wants to write his own story. When he calms himself down and puts his head to it, he can write a pretty cool story.’’

That story’s already in progress, and it already has a title.

Don’t wait to do something.