Day closed with a three-under-par 69 at TPC Scottsdale to finish seven shots behind American Scottie Scheffler, who successfully defended his maiden PGA Tour title to regain golf's top ranking.
But at 12 under, Day recorded his sixth top-20 finish from his past eight starts to secure another significant rankings boost.
The former world No.1 dropped out of the top 100 last year but is slowly building belief again after endless swing adjustments and a debilitating back injury.
His fifth in Phoenix, where 18 of the world's top 20 players teed up, set Day rocketing 34 places up the rankings to 57th.
Without a win since 2018, it seemed the 35-year-old would need to break his five-year title drought on the PGA Tour to earn an invite back to Augusta National, where he was a perennial contender for almost a decade.
But he's now within striking distance of punching his ticket to the Masters with a return to the top 50 by the end of next month.
Tellingly, Day finally feels like he's heading in the right direction again after regaining faith in his swing following adjustments to help him manage a debilitating back injury.
"I feel pretty good about how things progressed over the week. I feel that the swing is starting to feel a lot more comfortable," Day said.
"Which is good because at the start of the week I didn't have a lot of confidence in my swing.
"I actually texted my buddy playing down in Australia. I said, 'My swing, I'm not really confident in it'.
"I just kind of was grinding away and I finished fifth."
Once revered for having the best short game in golf, a tag that now sits with fellow Australian Cameron Smith, Day is also growing more and more confident on and around the greens.
"The putting's nice. Short game's looking really good,. Good form going into next week," Day said ahead of this week's $A29 million Genesis Invitational in Los Angeles, where Tiger Woods makes his return in another high-class field.
The one-time major champion is also feeling mentally revitalised after admitting he was not in the right head space to challenge for golf's big trophies in the past couple of years.
"You're playing against the best players in the world, but sometimes it's just you don't believe in yourself and you kind of lose trust in your ability," Day said.
Countryman Lucas Herbert tied for 50th on Sunday at one under, following a final-round 70.
Fellow Australian Rhein Gibson, meanwhile, took a giant stride towards regaining his PGA Tour card next season with a four-shot victory at the secondary Korn Ferry Tour's event in Bogota, Colombia.
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