McIlroy has won the European Tour’s season-finale twice and never finished worse than 11th in seven appearances at Jumeirah Golf Estates, with a 72 in 2010 his worst score in 28 rounds.
However, the world number two could only manage an opening 75 on Thursday to lie joint 55th in the 60-man field, nine shots behind Ryder Cup team-mate Westwood.
It took McIlroy 14 holes to register his first birdie of the day and although he swiftly added another on the next, the four-time major winner double-bogeyed the 16th after needing two attempts – the second minus his right shoe and sock – to play from the edge of a water hazard.
In contrast, Westwood carded seven birdies and just one bogey to match his opening 66 in the inaugural event in 2009, which he went on to win by six shots to become European number one for the second time.
“That’s certainly in the top two or three performances in my career,” Westwood said. “Maybe even the best performance of my career, knowing that I needed to win to beat Rory in the Race to Dubai, and did that by six and pretty much dominated the field over the weekend.
“Today was as good as I’ve played for quite some time. I’ve found a couple of keys in different parts of my game and I’ve been working on them hard and it all came together today.”
Westwood had been due to make his World Cup debut in Melbourne next week, but with Danny Willett pulling out to protect a back injury, Ryder Cup team-mate Chris Wood took his place as the next highest English player in the world rankings at the end of July.
Under tournament rules, Wood was also able to select his partner and opted for Andy Sullivan, much to Westwood’s disappointment.
“I’ve been looking forward to it for a few months now, so it’s frustrating,” said the 43-year-old, whose frustration was probably heightened by seeing Wood and Sullivan shoot 75 and 76 respectively.
“I’m disappointed not to be playing. I can understand him picking a mate and he’s picked a very good player. It’s probably more to do with the rules than anything.
“I think the week before somebody is meant to go down there is a little late to say, no, you’re not playing.
“I needed to be higher in the world rankings to pick my partner and if I’m higher next year Woody probably shouldn’t be expecting a pick!”
Westwood’s former Ryder Cup partner Nicolas Colsaerts and France’s Julien Quesne shared second place on five under, with Sergio Garcia, Francesco Molinari and Joost Luiten a shot further back.
Colsaerts carded five birdies in a flawless round but was disappointed not to go even lower, adding: “When you play that well you want to squeeze every shot you can out of it, but I’m confident I can keep rolling like this.
“This is probably the one course out of the three in the Final Series that suits my game the best. There’s corners I can take on. I can use my length as a big advantage to come in with shorter irons into greens, especially the way the greens are designed.
“This is the one that I had my eyes on and I know that if I bring the game that I’ve been displaying all year out here on this course, it should be a decent recipe.”
Race to Dubai leader Henrik Stenson, who has a lead of 299,675 points over Willett, managed just one birdie in an opening 72, with Willett and Alex Noren both one shot better off.
