Porter, who has led or shared the lead in each of the first two rounds of the joint Nationwide-Australasian PGA Tour event, had a 7-under total of 209 on the Moonah Links.
Australians Terry Price and Wayne Perske were one stroke back, Price after a 70 and Perske after a 72. Tee McCabe of the United States was in fourth place, two back of Porter.
Two Americans were tied for fifth, D.J. Brigman (68) and Fran Quinn (71), who trailed Porter by one stroke after Thursdays opening round.
Porter injured his neck on Saturday morning while working out and said he seriously considered pulling out.
My body was already a little bit stiff, Porter said. Id already run on the treadmill, done a couple of different exercises and then I was doing some lat pulldowns.
Ive had this injury a couple of times in the past and its something Im going to have to look at. Every time I seem to do a few weights above my head this occurs.
Porter said a physiotherapy session didnt help, but the pain lessened with some anti-inflammatory tablets.