While a lacklustre McIlroy managed only one birdie to be just inside the top 100 on three over par, little-known Spaniard Javi Colomo produced a superb 64 to lead compatriot Miguel Angel Jimenez and Australian Andrew Dodt by one stroke.
Colomo qualified for the event off his Asian Tour ranking, having failed to come through the European qualifying school on three occasions.
The 28-year-old actually began with 10 pars in a row, but five birdies in the next six holes brought him alongside Jimenez and after completing a front-nine 29 he finished his day's work with a four-foot putt for yet another birdie at the 367-yard 10th.
McIlroy was hoping to put even more of a gloss on a season in which he has won his second major title and topped the money lists on both sides of the Atlantic - a feat nobody had achieved until Luke Donald did it last year.
But he began with a bogey, turned in one over, made a mess of his approach to the 14th and three-putted from the fringe of the next.
It could so easily have been Jimenez's day but after seven birdies the 48-year-old, twice a winner of the title and now trying to become the European Tour's oldest-ever champion, finished with two bogeys.
"I'm putting very well and it's a pity I missed a fairway on the ninth and then on the last got a big flyer," Jimenez said. "It's an old-fashioned course - not very long, but you need to be very precise."
He was playing with fellow countryman and Ryder Cup captain Jose Maria Olazabal, who in a return to form shot 66.
Scot Paul Lawrie stood three under until going in the water at the last and double-bogeying, while playing partner YE Yang - Asia's only major champion in the men's game - reached five under before also finding the lake and bogeying to be four under alongside Olazabal, China's Zhang Lian-wei, Swede Fredrik Andersson Hed and Italy's Lorenzo Gagli.