After spiralling to 175th in the rankings in late 2022, Australia's former world No.1 has restored his body and game to the levels needed to contend at major championships.
A tie for eighth at last year's Masters after a runner-up showing at the 2023 British Open and a drought-breaking 13th PGA Tour victory in between attest to that.
But after five seconds, a third and three fourths from a total of 10 top-five finishes at golf's four biggest events, a revitalised Day still yearns for much more than an elusive second career major.
After reuniting this year with long-time coach Col Swatton, the mentor knows how hard Day has had to work to overcome debilitating back issues to rediscover his love and dedication for the game.
"Unfinished business in getting back to the No.1 player in the world, I think that's definitely on his radar," Swatton said before Thursday's first round at Quail Hollow.
"When you reach the highest of highs and you become the best player in the world, then suddenly you get to the top of the mountain and you go, 'OK, well that's great, and it smells a little different up here and it looks a little bit different'.
"Then you sort of start to figure it out, you have a few injuries and everything else.
"But I think for Jase, he's got his heart set on trying to be fully exempt for a lifetime on the PGA Tour - and that's 20-plus wins.
"So that's probably somewhere in his radar, and also too Jason's in a different place now. He's got five kids. He's got a lot going on."
The 35-year-old enters the PGA Championship a little underdone after withdrawing from the CJ Cup with a neck injury.
But Swatton is not the least bit concerned.
"He had some challenges last week that he's back on top of and he's feeling good going into this week," he said.
"Is he a little under-prepared? Maybe.
"But also, too, don't forget that's when Jason Day plays his best golf; when he feels his back's against the wall.
"So he's going into this week feeling a little under-prepared but, at the same time, I can name five events that we've won being under-prepared, all big ones.
"So don't count Jason Day out."
Day will be the first Australian to hit off on Thursday night at 2139 (AEST) alongside fellow former PGA Championship winner Phil Mickelson and English star Tommy Fleetwood.
Countrymen Min Woo Lee and Karl Vilips are also off in the morning wave in North Carolina.
Adam Scott, Cameron Smith, Cam Davis and Elvis Smylie all have afternoon tee times for round one.
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