The oldest rider in the field at 35, Melandri (Ducati) passed long-time leader and polesitter Tom Sykes (Kawasaki) on lap 19 and stayed in front for the rest of the 22-lap race.

In a fast-paced battle from the outset, he won by 1.18 seconds over Sykes, with Chaz Davies (Ducati) a further eight seconds back in third position.

It was Melandri's 21st victory in WorldSBK competition and his first at Phillip Island. He's also won grand prix races at the venue in the 125cc (1999), 250cc (2002) and MotoGP (2006) classes.

"To win the first race of the season is amazing," said Melandri.

"It was a very difficult race. Tom set an amazing speed during the first part of the race but, after a year back with Ducati, I am much more aware of my potential.

"For sure, the other riders will be stronger tomorrow (Sunday), and a lot will depend on the weather."

Ducati's last WorldSBK win at Phillip Island was in 2013 with Spaniard Carlos Checa. Overall, Ducati have 23 wins at Phillip Island, with Aussie legend Troy Bayliss a major part of that success.

Sykes' rear tyre called it a day with five laps to go, but he was still delighted with his performance.

"This is the strongest start to any season in my career," said Sykes.

"Marco put in a strong race, and I knew he would be there at the end. Still, I tried to break him about two-thirds distance in but he just had a little bit better tyre and rode it home."

Spaniard Xavi Fores (Ducati) finished fourth ahead of world champion Jonathan Rea (Kawasaki), who circulated in second position for more than half the race before his pace dropped away alarmingly in the last few laps - he was easily passed by Davies and Fores on the second-last lap.

Alex Lowes (Yamaha), Leon Camier (Honda), Eugene Laverty (Aprilia), Michael van der Mark (Yamaha) and Leandro Mercado (Kawasaki) completed the top 10.

There were 16 finishers and five retirements - including Jordi Torres (MV Agusta) and the Aussies Wayne Maxwell (Yamaha), Troy Herfoss (Honda) and Daniel Falzon (Yamaha). Maxwell crashed on lap two, while his compatriots were forced out by technical problems.

The award for the biggest exit went to Columbian Yonny Hernandez, who was spat off hard at turn six.

Italian Lorenzo Savadori (Aprilia), who was the fastest man on track on Friday, didn't start after breaking his collarbone early on Saturday afternoon in qualifying.

Australian Associated Press