Elvis Smylie had the overnight lead after a six-under 65 in clearer skies earlier on Thursday, while local stars Jason Day, Cameron Smith, Marc Leishman (67) and Min Woo Lee (68) sat just off the pace.
Rain returned to the sodden course to make life difficult for the afternoon groups.
Elvis Smylie's final-hole chip-in gave him the first-round lead in Brisbane. (Dave Hunt/AAP PHOTOS)
But Perez - fourth at his home Olympics in Paris this year - didn't seem to mind.
A solitary bogey was his only blemish in a round of 66 matched by Matias Sanchez, Swiss talent Joel Girrbach and Chile's Cristobal Del Solar, who birdied four of his last five holes.
"It's a lot easier when you're playing well," Perez said of playing in the rain.
"These conditions can really create some separation, but it doesn't bother you as much as it would if you're off your game, when every little thing becomes marginally a disadvantage.
"Everything seems to bother you more when you're not playing as well."
Perez didn't want to think about his early rise before a 6am Friday tee time, although he had checked the forecast and was encouraged.
"We should get more of the good draw, with some rain coming in the afternoon," he said.
"It will be nice to come out and put on a good round early, but who knows."
Brisbane pair Jason Day and Cameron Smith are in the mix at their home tournament. (Dave Hunt/AAP PHOTOS)
Smylie made eight birdies to set the pace on Thursday, after defending champion Lee had surged to five-under through 12 holes.
But he regretted some loose play to fall back into the pack.
Smith, Day and Lee will partner again in the marquee group on Friday afternoon.
Weather is expected to improve for the weekend and provide some respite after a week of downpours forced grounds staff to work overtime.
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