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On a damp track, Yamaha duo Alex Lowes and Michael van der Mark made the best starts, and led the way along the straight approaching the Adelaide hairpin after leapfrogging poleman Leon Camier.
From sixth on the grid, van der Mark led at the hairpin but lost ground just as quickly, as he fell behind Lowes, Camier and the Ducati of Davies over the course of the next lap.
Lowes could only hold on to the lead for three laps before Davies took over, the Welshman then consistently pulling away.
Camier meanwhile seemed to be in a strong position to finally claim MV Agusta's first podium in the series, only for his bike to dramatically slow down.
However, his retirement did not guarantee Lowes second, as a recovering van der Mark immediately started to put pressure on his Yamaha teammate.
The Dutchman couldn't make a move, though, and Lowes eventually lost him and even closed the gap to Davies.
He cut the lead from five to three seconds before taking the chequered flag, as Davies collected his seventh win of the year.
Van der Mark held on for third, securing Yamaha's first double podium since its return to WSBK last year.
Barni Ducati's Xavi Fores was a distant fourth, with Lorenzo Savadori looking set to take fifth before a mechanical issue on the final lap forced him out of the race.
Savadori's Milwaukee Aprilia teammate Eugene Laverty also failed to score, as he fell at the end of the second lap.
The Irishman's crash also affected Rea, who clipped Laverty's bike, and damaged his rear brake. That forced the Kawasaki rider, who sealed the title in Saturday's first race, to pull into the pits and retire.
Savadori's woes promoted Marco Melandri to fifth, the Ducati rider winning a race-long duel with Leandro Mercado (Ioda Aprilia).
Rea's teammate Tom Sykes had a quiet race in seventh, while Althea BMW duo Jordi Torres and Raffaele De Rosa were eighth and 10th respectively, sandwiching Roman Ramos (Go Eleven Kawasaki).
The Ten Kate Hondas of Davide Giugliano and Jacob Gagne finished behind in 11th and 12th.
|3||Michael van der Mark||Yamaha||4.556|
|10||Raffaele De Rosa||BMW||35.227|
|17||Eugene Laverty||Aprilia||1 lap|
|18||Ondrej Jezek||Kawasaki||2 laps|
|Leon Camier||MV Agusta|
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