The Northern Irishman edged ahead of Welsh rival Chaz Davies on the last of the 22 laps to clinch his third successive win in Australia.
Rea's British and Kawasaki team-mate, Englishman Tom Sykes, was third.
"It was a little bit like a bicycle race and no-one wanted to put their nose in front," Rea, 30, said.
The champion's victory - his 39th in WSB - ended Davies' six-race winning streak from 2016.
Rea is one of four riders to clinch back-to-back Superbike titles but is aiming to become the first to win three in a row.
He still lies two titles behind Carl Fogarty's record of four championship successes.
Toomebridge man Eugene Laverty, who is back in the series after two campaigns in the MotoGP paddock, finished eighth on his Milwaukee Aprilia.
There will be a second Superbike race at Phillip Island on Sunday.

Operations are due to resume early next week after a meeting between NHS bosses and other partners on Thursday night.
Data suggested death rates there were double that of other centres, but experts have questioned their accuracy.
However, the Department of Health (DoH) said the NHS was right to investigate safety at the unit.
A spokesperson said: "We support NHS England and the trust in their decision to suspend surgery last week on the basis that there were serious concerns that needed to be investigated.
"If the trust and the regulators are content that these concerns can now be explained or addressed then we would support a joint decision to resume surgery."
Leeds Teaching Hospitals NHS Trust said work would be done over the weekend to give "sufficient assurance" the unit is safe to reopen, early next week.
Doctors and other medical experts said the data on death rates had not been verified and was not fit to base a decision to close the unit on.
Mortality data and staffing are just two of the concerns being looked at as part of a review into why children's cardiac surgery at Leeds General Infirmary was suspended last Thursday.
Leeds Teaching Hospitals NHS Trust, NHS England and the Care Quality Commission have all been involved.
The indication is that if the trust can provide strong assurances that heart surgery is safe, then the unit could reopen early next week.
But discussions will continue over the weekend as part of the review, which is expected to last three weeks.
If the unit does reopen, Leeds General Infirmary will have to reassure patients and families that safety of care is paramount.
The NHS can ill afford another scandal after Mid Staffs.
Yet Health Secretary Jeremy Hunt will probably have the last say on the future of children's heart services, at Leeds and elsewhere.
A separate independent review is set to report to him on the whole restructuring of children's heart services in England.
But, Sir Bruce Keogh, the medical director of NHS England, said the figures were among a "constellation of reasons" the decision was made.  He has been backed by health secretary Jeremy Hunt.
A senior Westminster source has told the BBC that "as far as the secretary of state is concerned, Sir Bruce Keogh was right to ask questions about the safety of heart surgery at the unit".
Parents had criticised the timing of the suspension of surgery at the unit, which came 24 hours after a High Court judge ruled that a decision-making process to close it as part of an England-wide reorganisation of services was "legally flawed".
Stuart Andrew, the Conservative MP for Pudsey, called for "some really serious investigating" into the decision to suspend surgery.
Mr Andrew claimed a review of the mortality figures showed "Leeds is within the average and is a safe unit to use".
He said recent events raised questions about the NHS decision to close the Leeds unit for good and concentrate children's heart surgery in fewer centres.
"We are losing faith in that review process," said Mr Andrew.
"Some of these people are the same people on that decision-making body."
Lois Brown, whose five-year-old daughter had life-saving heart treatment at the hospital, described the decision to restart surgery as "fantastic".
Ms Brown has been involved in the campaign and court action to save the unit from closure.
She said she wanted answers as to why the unit was shut.
"I'm really relieved that children are going to get surgery at Leeds again," she said.
"For the past week and a bit we have been putting children's lives at risk for no reason, apparently."
Defending world champion Jonathan Rea has won the opening race of the 2017 Superbike World Championship at Phillip Island.
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Children's heart surgery is set to restart at Leeds General Infirmary, a week after it was claimed data showed higher-than-usual death rates there.