Jonathan Rea is chasing the first World Superbike clean sweep at Phillip Island since 2011 after beating fellow Briton Chaz Davies in a final-lap dogfight.
Davies for Ducati passed Kawasaki's Rea at turn 10 on Saturday, but the world champion blasted back at the next bend and kept the lead to the end, winning by 0.063 seconds.
Michael van der Mark took third position on his Honda.
The opening race of the season was Rea's 30th World Superbike win.
"It was a difficult race because I was at the front for most of it," he said.
"Every lap was '+0' on the board and by the end I was making my personal best laps but Chaz was still there.
"I attempted to close the door but left it a little open at MG (turn 10). Then when Chaz ran a little bit wide I was able to square off and move back into the lead and take the win - a great way to start the season.
"I am really happy and looking forward to tomorrow's race."
Rea started the 22-lap race in pole position, along with Davide Giugliano (Ducati) and Kawasaki's Tom Sykes, who earlier set the fastest-ever World Superbike lap with a ride of 1min 30.020sec.
Sykes was the only rider other than Rea to lead the race, but he was shuffled back to sixth position during the space of three laps in the middle of the race and could not work his way back.
Italian Giugliano set the fastest lap of the race (1:31.445) on the final 4.448km circuit.
The leading Australian was BMW Motorrad's Josh Brookes in 10th position as he contested his first World Superbike race in almost a decade. The second Australian was Ducati rider Mike Jones in 14th place.
"We've got a good base to build on and we have to keep the developments coming," Brookes said.
"There was good work done on the bike overnight for today, so we know the improvements are working.
"Considering how we started the week, top 10 is OK and to have our first points is nice, but it's not where we want to be.
"Now that we've got data and my input from race one, I hope we can make further changes that will be more productive."
The weekend's second race is at 3pm (AEDT) on Sunday.