Jonathan Rea took full advantage of Chaz Davies stumbling in qualifying and Tom Sykes withdrawing from the weekend to win the first World Superbike race at Portimao with ease.
While Rea started from pole, main rival Davies made a mistake in qualifying and lined up only ninth.
With Rea's Kawasaki teammate Sykes withdrawing after a Saturday morning practice crash, he was joined by Aprilia duo Eugene Laverty and Lorenzo Savadori on the front row.
Rea led off the line and immediately pulled away from the rest of the field, led by Laverty.
Davies gained five positions at the start to run fourth and quickly passed Savadori and Laverty to run second by lap 5.
However, by the time he worked his way through the field, Rea was leading by nearly five seconds clear, and the Ducati rider was unable to close the gap. Rea eventually crossed the line with a lead of 6.1s.
Melandri also quickly passed Laverty but couldn't keep up with Davies, and was instead under pressure from MV Agusta's Leon Camier in the latter stages of the race.
Camier got past Laverty halfway through the race and gradually closed in on Melandri, but eventually ran out of time and settled for fourth, his best result of the season.
Yamaha's Michael van der Mark kept up with Camier to grab fifth, followed by Jordi Torres (Althea BMW).
The Aprilias of Laverty and Savadori both lost five places compared to their starting positions to finish seventh and eighth respectively.
The top 10 was completed by Spaniards Xavi Fores (Barni Ducati) and Roman Ramos (Go Eleven Kawasaki).
Honda's Stefan Bradl had a strong start to run sixth after Lap 1, but crashed at Turn 14 soon afterwards, as Alex Lowes became another notable rider to fall later on.
Takumi Takahashi finished 15th on his WSBK debut on the second Honda, 54 seconds off the lead.
|4||Leon Camier||MV Agusta||10.508|
|5||Michael van der Mark||Yamaha||13.739|
|11||Raffaele De Rosa||BMW||43.181|
|18||Alex Lowes||Yamaha||1 lap|
|Ret||Leandro Mercado||Aprilia||4 laps|
|Ret||Stefan Bradl||Honda||18 laps|