"Obviously, the preparation and the hard work over the holidays has really paid off early, so I need to make sure I stay on top of that."
There were numerous subplots to Day's victory.
His caddie for the week is his friend from childhood, Rika Batisbasaga, who was pulled into duty because Day's regular caddie had visa problems.
Day was struggling with a sore back before the tournament and his prospects didn't look good when he was 3 over on the South Course on Thursday through the first 12 holes.
Day also revealed that he had a Saturday night conversation with Tiger Woods about how to manage "momentum."
"His piece of advice was to not make bogey," Day recalled with a laugh, knowing full well that was a near-impossible task on Sunday, when the Santa Ana winds blew to at least 20 mph at times.
On top of all that, Day had taken a long break from competition, and was coming off a 2017 season in which he had only five top-10 finishes and saw his world ranking drop to 14th after he spent 51 weeks at No. 1.
Too, personal turmoil dogged Day. His mother was diagnosed with lung cancer, late in the year he decided to no longer have his coach and mentor, Colin Swatton, on the bag, and Ellie Day suffered a miscarriage on Thanksgiving.
"Last year was a good kick in the butt, not really being talked about ... and being talked about for the wrong reasons," Day said. "Take my mum out of the equation. I see the guys winning -- Jordan (Spieth) and Dustin (Johnson) are playing some tremendous golf. Jon Rahm's playing some tremendous golf, and I feel like I should be there, as well, winning.
"Last year I felt mentally stressed, but also run down, burnt out," Day said. "It was hard for me to be on the golf course. But this year my whole mindset's different. I'm very motivated to get back to the No. 1 spot, and I know that the only way to get back to the No. 1 spot is win, and that's what I've just got to do."