The world number three from Northern Ireland posted a first round six-under par 66 to lie two shots bwhind American amateur Bryson Dechambeau (64) with Henrik Stenson of Sweden in second after a 65.
NcIlroy made two bogeys but compensated with eight birdies. Spieth, who uncharacteristically missed a couple of short putts, also had two bogeys in his round of 68.
World number six Rickie Fowler, the third player in the morning feature group, opened with a two-under par 70.
McIlroy is playing his first tournament of 2016 - after a gap of almost two months since winning the DP World Tour Championship in Dubai in November - but showed no signs of ring rustiness as he opened with two straight birdies on the 1h and 11th holes after starting on the back nine of the golf course.
However, the putter took some time to warm up as he dropped two shots on his first nine - on the 13th and 17th holes - both because of three-putts.
Spieth, who won the Tournament of Champions on the PGA Tour a couple of weeks ago, needed six holes to make his first birdie, but then added six more.
The two bogeys came on the second and fifth holes, but the defending Masters and US Open champion seemed most frustrated by a missed birdie putt from four feet on the eighth hole.
Stenson, who had a surgery done on his right knee in December, had said his first challenge would be to walk the 18 holes this week.
But with his iron play on song, the 39-year-old Swede had absolutely no trouble throughout the day.
The world number five, who holds the course record of 62 in Abu Dhabi, closed with a bogey after failing to make an up-and-down from the bunker on the ninth hole, but that was his only blemish.
He looked set for the first round lead until Dechambeau, who eagled the par 5 8th hole, grabbed top spot with a birdie, his seventh, at the last.
England's Richard Bland came in with a 67 which included a lone bogey in his penultimate hole, the 17th of the course.
Three-time Abu Dhabi champion Martin Kaymer, who lost a 10-shot lead over the last 10 holes on the final day last year, made a decent start with a three-under par 69. – AFP
Original source: McIlroy gains early edge over Spieth