American Fran Quinn is alone in second place at minus-4 on the Open Course at Moonah Links.
Chris Kirk and Fabian Gomez, who had gotten to minus-5, but posted three bogeys on his second nine, are one stroke further back at 3-under-par 69.
Despite the wind growing stronger as the day went on, the top four players on the leaderboard all played in afternoon groups.
Porter was even par after nine holes as he birdied the second and bogeyed the fourth. He parred the other seven holes on the front nine.
Around the turn, Porter caught fire. He converted a birdie try on the 10th. After two pars, he flew up the leaderboard.
Porter birdied the par-3 13th and came right back to birdie 14. He was not finished as he also birdied the 15th to take the lead.
The Australian made it four in a row with a birdie on the 16th to secure the first-round lead at minus-5.
'I surprised myself,' Porter admitted. 'I said to my caddie 'that if you chase birdies they never come'. So I just did a really good job of staying in the present today.'
Quinn played the back nine first and got off to a quick start with birdies on 10 and 11. After tripping to a bogey on the 16th, Quinn came right back to birdie the 17th.
The American tripped to another bogey on 18 to make the turn in minus-1. He converted back-to-back birdies from the first to move up the leaderboard.
Quinn faltered to a bogey on No. 4, but he atoned for that mistake with a birdie on the sixth. Quinn moved into second place as he birdied the eighth to finish at minus-4.
'The conditions were pretty difficult. The wind was blowing and there were a lot of cross winds,' Quinn stated. 'There were a lot of difficult shots, difficult cross winds. I drove the ball exceptionally well all day.'
There is a large group of players tied for fifth place at 2-under-par 70. Americans Tee McCabe and Matthew Every were joined there by Australians Rick Kulacz, Paul Marantz, Terry Price and Paul Sheehan, as well as New Zealander Mahal Pearce.
Among the nine players tied for 12th at minus-1 are 2002 U.S. Amateur champ Ricky Barnes and Michael Putnam.