The 29-year-old American picked the right time to end nine holes without a birdie, even as so many others were making them to create a four-way tie for the lead.
Hitting a six-iron to five feet, he holed out for birdie on the 18th hole at Sea Island for a two-under 68, winning at 16 under.
The victory came in his 134th start as a pro, and gets him into three $US20 million events over the first two months of 2025, along with his first trip to the Masters.
Daniel Berger (67) missed a 20-foot birdie attempt on the 18th that preceded McNealy's winner. He tied for second with Colombia's Nico Echavarria (65) and fellow American Luke Clanton (66), both of whom missed par putts from inside eight feet on the final hole that created the four-way tie.
Berger got a small consolation prize, moving inside the top 125 to keep a full PGA Tour card for 2025 when the fields will be smaller and only the top 100 will keep cards.
Henrik Norlander, who was No.126 in the FedEx Cup last year, had a 63-68 weekend and joined Berger as the two players who moved into the top 125.
For Joel Dahmen, it was a matter of staying there.
He was at No.124 coming into the final tournament, had to make a 5-foot par putt just to make the cut on the number and then delivered a tee-to-green clinic — along with holing a 113-yard sand wedge for eagle early in his round — for a closing 64. It was enough to stay at No.124 with nine points to spare.
"Two of the biggest pressure moments of my career I showed up, and I can take that going forward," Dahmen said.
Clanton was a shot away from joining Nick Dunlap as amateur winners on the PGA Tour this year.
Clanton, who has taken over as the top-ranked amateur in the world, now has two runner-up finishes and four top 10s in the seven PGA Tour starts the last five months.
He had the look of a winner when he poured in birdie putts on the 14th and 16th holes to tie for the lead. But he tugged his approach to the 18th into bunker, blasted out nicely to 7 feet and stooped over in disbelief when he missed his par putt.
"It's going to be a tough one to definitely take, for sure, after bogeying the last," Clanton said. "But I think it's proven to me that out here I can win, so I'll be training for that."
Echavarria, who won in Japan a month ago, had not made a bogey all day until going long on the 18th, chipping to 9 feet and catching the lip with his par putt.
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