It left the world No.3 five shots off the lead held by his Ryder Cup teammate Tommy Fleetwood in the first event of the European tour play-offs on Thursday.
Seeking a victory that can clinch a sixth year-long Race to Dubai title, McIlroy returned to competitive action after a month away — most of which he spent shut away in a studio hitting balls against a screen in search of a more robust swing that can hold up in pressure-filled moments.
McIlroy didn't make too many mistakes in his first round, save for pushing his tee shot on the par-three 17th and failing to get up and down for par. That was his only bogey, while he made six birdies — including a tap-in at the last.
"It felt OK," said McIlroy, looking rather unimpressed. "I've gotten comfortable doing this little rehearsal before I take the club back. It felt fine. I probably wasn't as imaginative out there — I was hitting very straight shots.
"I hit a couple where I didn't see the picture of what I was trying to do with the ball flight because I was thinking a little too much about what I was doing with the swing."
McIlroy said the lack of wind and the generous size of the fairways at Yas Links made his task easier and allowed him to focus on his modified swing.
"I am quite fortunate that it's a nice week to come back," he said.
Fleetwood — the next highest-ranked player in the reduced 70-man field at No.10 — was more in the zone, making eight birdies to go with an eagle at the par-five second hole in a bogey-free round of 10-under 62.
The Englishman took the solo lead for the first time by rolling in a birdie putt from 10 feet at the last hole.
Fleetwood was a stroke clear of Thorbjorn Olesen, of Denmark, and Johannes Veerman, of the United States, with Briton Tyrrell Hatton — a LIV Golf player — in a share of fourth place after shooting 64 with Laurie Canter, Paul Waring and Francesco Laporta.
McIlroy, who was in a tie for 18th, has a huge lead in the Race to Dubai standings and can win what was formerly the Order of Merit title with an event to spare with a victory in Abu Dhabi.
That would take some suspense out of the season-ending World Tour Championship in Dubai next week.
McIlroy has finished a season as the European No.1 five times and can tie the late Seve Ballesteros with a sixth. Colin Montgomerie has a record eight.
Min Woo Lee and David Micheluzzi led the Australian challenge with three-under par 69s leaving them tied for 35th, while Adam Scott as a couple of shots further back in joint-55th place following his 71.
