It brought for McIlroy a 'Dubai Double' as earlier in the year he won the Dubai Desert Classic. He also became the DP World Tour champion for the second time and the European No 1 for the third time.
But for India's Anirban Lahiri (71), the tournament ended at tied 34th place.
McIlroy (66) totalled 21-under 267, while Sullivan (68), who won three times this year, aggregated 20-under 268. Lahiri was tied 34th at five-under 283 in his maiden appearance at the DP World Tour Championships.
Lahiri, who was troubled by an niggle in his knee, once again had six birdies during the day - the same as the third round - but gave away a lot with five bogeys. Overall, there were 22 birdies for him during the week, but a lot of that was undone by 13 bogeys and two doubles.
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"I think of all the four days I played the best golf today. I played much better but I got unlucky on many holes. I got some bad kicks here and there like on 16th. I felt some signs of form which I have not felt since Hong Kong. And, the knee feels a lot better, but overall not a great week obviously," said Lahiri.
It was once again an up-and-down round. A birdie on second was followed by back-to-back bogeys on third and fourth. Birdies on seventh and 10th indicated his "better" frame of mind, before he got a couple of bad breaks on the remaining stretch as he gave away some gains.
He added,"It was disappointing, because this golf course very accessible. It is perfect for me, like the Jaypee Greens (in India), which is among my favourite in terms of grass and so on. This week, I was nowhere even my 'B' game."
Lahiri's next event, which will also be his last of 2015, will be the Hero World Challenge in Bahamas starting on December 3.