The Australian, 28, led from start-to-finish but there were tough times -- and when he needed strength, it was Woods's words of wisdom echoing around his head.
"Be yourself, stay in your world," was Woods's mantra. He should know -- the former world No. 1 won eight times at Bay Hill.
It worked, as Day ground out victory by one shot from American Kevin Chappell in Orlando, Florida.
Day's eighth PGA Tour title lifted him one place above Rory McIlroy in the world rankings to No. 2 behind Jordan Spieth.
And it reconfirmed his status as one of the favorites for the U.S. Masters at Augusta next month despite a lackluster start to the season.
Day has turned to the injured Woods for advice on numerous occasions of late, and the pair were in touch throughout the tournament hosted by the 86-year-old Palmer.
"We were trading texts back and forth all week, obviously words of wisdom because he's played well here," Day told his victory news conference.
"It's the same thing. Just be yourself and stay in your world.
"But to be able to hear what he has to say and his advice and how much he believes in me really means a lot, especially coming from the best.
"It gives me so much confidence that a person like that would believe in me, especially as a kid I was idolizing him ever since watching him in '97 win the Masters for the first time and all of a sudden I'm playing the Tour and I'm pretty close with him now."
Day led by two shots going into the final round but stumbled early on and trailed Chappell by one shot with two holes left.
But he drained a 12ft putt for a birdie on the 17th and saved par from a greenside bunker on the 18th to edge home at 17 under par.
Sweden's Henrik Stenson and American Troy Merritt were tied for third on 14 under. McIlroy was tied 27th, Spieth took the week off.
'Patience and aggression'
Day won the U.S. PGA Championship at Whistling Straits last August for his first major title, and rose to world No. 1 for a spell amid a stellar end to 2015, which also included victories in the Barclays and BMW Championship in the Fed Ex Cup playoffs.
However, with a media desperate to hype up a new "Big Three" in golf -- with Day, Spieth and McIlroy emulating the rivalry of Palmer, Jack Nicklaus and Gary Player -- Day's form, dipped with nothing better than a tie for 10th in his first four starts this term.
But employing another Woods-esque mantra, "patience and aggression," Day was able to do something the 14-time major champion has never achieved at Bay Hill -- win from wire to wire.
"I never knew that and I will text him that tonight," he said. "You know, regardless if you win wire to wire or you win pretty or you win ugly, a win is a win.
"Everyone was asking what's wrong, what's going on, why aren't you playing well?
"I just kept on saying to myself, kept on saying to the people, the fans, the media, just be patient, I'm just going through the process and I'm going to keep working hard. Things take time."
Day finished runner-up in the Masters on his debut in 2011, and was pipped to the honor of becoming the first Australian to win at Augusta when he came third behind countryman Adam Scott in 2013.
With the halfway lead Friday at Bay Hill, Day knew he was heading in the right direction.
"I really feel like I'm trending towards a really good Augusta," he said.