While McIlroy found birdies hard to come by at times, Hidalgo had no such trouble as the 27-year-old reeled off seven in a row from the second.
After a bogey at the ninth, Hidalgo picked up four more shots in the first six holes of his back nine.
His momentum stalled with a double-bogey seven on the 16th after hitting his second into the water, but after steadying himself with a par on 17, he finished with a birdie four.
“I really feel for a few moments I was playing the PlayStation, to be honest,” said Hidalgo, who beat two-time major winner Jon Rahm in a play-off to win his national title last year.
“Every single shot was directly to the pin. Even the one I missed, it was directly to the pin, like the 13 one I go over, but it was straight to the pin.
“[I’m] so happy. Not going to lie, really, really happy. Obviously now you remember the 16th, but you need to remember the few recoveries I did. The one on 17 was pretty important, and obviously the birdie on 18 to finish with good feelings obviously for tomorrow.”
Saddier, however, was seemingly unaffected by Hidalgo’s stunning early move as the 33-year-old mixed seven birdies with three bogeys to hold the 54-hole lead and put himself in position to land a second DP World Tour title.
European Ryder Cup players Shane Lowry (70) and Tyrrell Hatton (71) failed to make a big move, while Northern Ireland’s Tom McKibbin carded just one birdie in a disappointing 74.