"I obviously could have shot a better score, but I did what I wanted to do, gave myself plenty of chances, just couldn't get the ball to drop", said McIlroy, after finishing equal fourth on 277, eight strokes behind Schauffele.
"And, honestly, I don't think anyone could have beaten Xander today".
That left him in joint-fourth position but eight shots behind the victor, Xander Schauffele, after the 25-year-old American covered his final 16 holes in 12-under-par to tie the course record with a closing 62 as he claimed a dramatic victory.
McIlroy has stated on numerous occasions he will focus his playing schedule around the PGA Tour in 2019, with the Northern Irishman pleased to test his game out so early in the year.More news: Apple cuts current-quarter production plan for new iPhones by 10%: Nikkei
He played the final round of the first major of 2018 with eventual victor Patrick Reed at the Masters but faded to finish equal fifth.
But on Sunday in Kapalua he may have been too patient as he started three off the lead but was overtaken from behind.
Having opened with rounds of 69-68-68 to find himself in the final group on the last day at Kapalua, the Northern Irishman was a touch disappointed to sign off with a one-under-par 72 in the event for 2018 winners on the USA circuit.
Schauffele won the Greenbrier Classic and the Tour Championship to lock up the PGA Tour's Rookie of the Year award in 2017, finished second in The Open last year and won the WGC-HSBC Champions after a play-off with Tony Finau last October.More news: Elon Musk called the launch date of Dragon-2 to the ISS
"I knew it was going to be a birdie-fest coming in".
On the 532-yard par-5 fifth, McIlroy had a birdie after hitting the green in 2 and two putting. "Jordan [Spieth] shot 30 under [in 2016], and I'm sure it wasn't windy that week".
The 25-year-old hit a similarly impressive approach at the last, a fairway-metal from 270 yards that he drew into the heart of the green before two-putting from 12 feet. "But, overall, it's been a positive week even though I wish I would have played a little better". "The next step is to go wire-to-wire, have a lead and maintain it".
"I have no idea what really works for me yet. I can't tell you what the winning formula is". "Frustrated right now but Xander played great, hat's off to him".More news: The DJI Smart Controller takes drone flying to new heights
Only five of the 33 players in the field shot worse than McIlroy's 1-under 72 in calmer conditions.