Porter was tied with Australian compatriot Wayne Perske, who moved up the leaderboard with a 67. The pair were at 6-under 138 on the Peter Thomson-designed Moonah Links course that hosted the Australian Open in 2003 and 2005.
Rick Kulacz was one stroke behind the leaders after a 69, while Terry Price shot a 70 and was at 4-under 140, two behind, to round out a sweep of the top four spots by Australians.
American Fran Quinn, a shot behind Porter after the first round, shot a 73 and was in fifth in the joint Nationwide-Australasian PGA tour event.
Drizzling rain fell throughout the day but it was the strong wind that affected most of the afternoon starters on the Mornington Peninsula layout outside Melbourne.
It was pretty windy out there in stages, Perske said. Im pretty happy with that score. I didnt make many mistakes and I could have gone a couple better.
Porter, starting on the back nine, was even-par for the day while making the turn. He had three straight birdies on the front nine along with two bogeys in the difficult conditions.
At the end of the day I am over the moon to shoot one under par because I really did not play that good, Porter said. I grinded it out. My short game, two days in a row, has held me in there.