It was the fourth title of the year for the Northern Ireland star in a 2015 which promised so much until he ruptured ankle ligaments in an impromptu game of football j
ust ahead of his defense of the British Open.
Since making a brave return at the U.S. PGA Championship, won by Jason Day
, McIlroy has been slowly working his way back to form, confirmed by his superb performance in Dubai.
A final round six-under-par 66 on the Earth Course at Jumeriah Golf Estates left him one shot clear of overnight leader Andy Sullivan of England on 21-under 267.
McIlroy trailed rising young star Sullivan around the turn, but a run of four birdies in five holes from the 11th secured him victory, salvaging a bogey on the 17th with a 30-foot putt after finding the water with his tee shot.
It was enough to clinch the Race to Dubai title for McIlroy for the third time in four years, his nearest challenger England's Danny Willett finishing in a tie for fourth in the European Tour finale on 13-under.
South African Branden Grace, who also had a mathematical chance of winning the Race to Dubai, finished third on 267.
"To be European number one for the third time in four years, that was a goal of mine at the start of the year. It was a goal of mine in the middle of the year and it was definitely a goal coming into these last few weeks," McIlroy told the official European Tour website.
McIlroy believes he is back to his best after his injury woes. "I think I'm right there. The only thing that's been holding me back over the past few weeks was my putting. My ball-striking's right where I want it to be. So I think I'm right there."
But already he is looking forward to 2016 to resume his rivalry with Spieth, winner of the opening two majors this year and so close in the two others, and Australian Day.
McIlroy needs to win the U.S. Masters to claim his career grand slam and has Augusta firmly in his sights.
"I think every time you go to Augusta, there's a lot of hype. There was a lot of hype around myself this year," he said.
"It's always going to be there until I get to put a Green Jacket on my back. It's obviously the first real goal of the year is to try and get ready for the Masters and be in as good of shape as possible going in there.
"And next year, the narrative might be around three guys, myself going for the grand slam again."
The win was worth $3.208 million for McIlroy -- $1.33 million for winning the DP World Tour Championship and a $1.875 million bonus for winning the Race to Dubai.
But he remains at world number three behind Day and Spieth despite the triumph.
Sullivan, bidding for his fourth win of the season on the European Tour, had the consolation of moving up to eighth in the overall money list.
He has also placed himself in a strong early position to claim a place on the European team for the Ryder Cup against the United States next year.
Rookie of the Year contenders South Korean Byeong-hun An and Matthew Fitzpatrick of England were in the six-man tie for fourth with Willett.