The Ardglass golfer, a European Tour invite, is three shots off the lead held by American Peter Uihlein.
Sharvin hit seven birdies but dropped three shots on par five holes, taking a double-bogey seven on the 15th.
Belfast's Michael Hoey finished on five over including two bogeys in the last three holes.
Ireland's Paul Dunne finished on one over.
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Sharvin slipped from five to three under, but made amends with a two at the par three 17th in Australia.
In what is only his second tournament as a professional, the 23-year-old expressed delight at his impressive start.
"This being my first European Tour event, it's really nice to post a nice number and see myself up the leaderboard with names I'm usually watching on TV," he said.
"My main focus this year is going to be Challenge Tour events and I can't think too far ahead, but I know if I play well I can compete."

The Transport for London (TfL) trial follows the success of its "Baby on board" badge for pregnant women.
TfL is recruiting 1,000 people to start wearing the blue badges from 12 September.
Mayor of London Sadiq Khan said he hoped they would "give confidence" to people who find standing difficult.
Some travellers, such as James McNaught who is joining the trial, had already started making their own badges to alert fellow passengers to their condition.
The 45-year-old designed "Cancer on board" badges after travelling on the Tube between Kentish Town and University College Hospital for chemotherapy.
Radiotherapy on his throat left him unable to speak to ask for a seat, and the morphine made him appear drunk.
"I'm really pleased TfL is doing this trial," he said. "A badge and card could help make a real difference to the lives of people undergoing drug treatment or with longer term conditions or disabilities."
TfL will use social media and customer information to encourage other passengers to look out for the badges.
"This small act of consideration from Londoners could make a huge difference to disabled people getting around the city and being fully involved in all London has to offer," said Alice Mitchell-Pye of charity Leonard Cheshire Disability.
The six-week trial is believed to be the first of its kind in Europe.
Cormac Sharvin made a superb start to his first European Tour event as a professional shooting a four-under par round of 68 at the Perth International.
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People with hidden health conditions are being offered "Please offer me a seat" badges in a bid to help ease their suffering on London transport.