A little over a year after losing his mum Dening to cancer and tumbling outside the top-100, Day denied Scottie Scheffler the chance to return to World No.1 in a tense Sunday shootout at TPC Craig Ranch.

Day fired a brilliant bogey-free final-round nine-under-par 62 to secure a steely one-shot win over Si Woo Kim (63) and American Austin Ekroat (65).

Kim's countryman C.T. Pan (62) was fourth at 21-under, with Scheffler (65) ultimately finishing fifth three shots back after being unable to stay with Day down the stretch.

Kim birdied the last to briefly join Day atop the leaderboard, but the Queenslander held his nerve to respond and deliver his wife Ellie – greenside and pregnant with the couple's fifth child – her own priceless Mother's Day gift.

In a poignant tribute, Day's caddy sported a bib with his mother's birth name, Adenil, and the inspired former World No.1 honoured her memory in style with his first tournament win since the 2018 Farmers Insurance Open.

"This was the first one (Mother's Day) kind of without her so to have her on my caddy bib was special," Day said.

Day celebrates his 72nd hole birdie to clinch his first Tour win in five years. PHOTO: Tim Heitman/Getty Images.

"And then obviously Ellie, the amount of sacrifices she's made for me and my career, I just can't thank her enough."

In a huge confidence booster ahead of next week's PGA Championship, the season's second major, Day finished at 23-under and had only three bogeys for the week.

Fittingly, the 35-year-old ended his barren run at the same tournament where he clinched his maiden PGA Tour win in 2010.

But his 13th triumph is even more special and completes Day's tumultuous journey back from heartache and despair.

He was languishing at 175th in the world last September before rebuilding his swing to combat the debilitating back injury that threatened to prematurely end a once-great career.

But the 2016 PGA Championship winner's resilience is now paying off, with Day among the hottest players on the planet once more.

He posted six top-10 finishes this year and eight consecutive top-20s before an untimely bout of vertigo cruelled his Masters' chances.

"This was the first one (Mother's Day) kind of without her so to have her on my caddy bib was special." - Jason Day.

As well as the trophy, the 35-year-old pocketed a cheque for US$1.7 million (A$2.6m) after snapping his 1,835-day title drought.

"It's been a struggling few years so to be able to get the win the way I played today was really special," Day said.

"I've had a lot of injuries with my back and for a moment there I thought I wasn't going to play again and then just trying to get through those two years and just trying to get through a tournament was difficult.

"So to be on the other side of it, being healthy, feeling good about my game, finally winning again, there's no better feeling really."

Day and Scheffler both started the round two shots behind co-leaders Ryan Palmer, Eckroat and China-born Dallas local Zecheng Dou, who moved clear early on Sunday.

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But the cream rose to the top after Dou opened the door with a double-bogey on 8th hole.

Day and Scheffler picked up four shots each to enter the back nine joint top at-18 under, with 22 players within three shots of the lead.

After hitting the hole with his approach on the 11th and darting off the green, Day had the golfing gods on his side when he chipped in for birdie at the next to claim the solo lead for the first time.

He was never headed.

Compatriot Adam Scott enjoyed the clubhouse at 19-under following an eight-birdie final-round 63 before eventually settling for equal seventh.

Aaron Baddeley (68) tied for 23rd at 15-under, Harrison Endycott the next best of the Aussies sharing 50th, while David Micheluzzi (70) finished at nine-under in a respectable share of 67th on his PGA Tour debut, Greg Chalmers a further shot back.