Miller crossed the line 0.105 seconds ahead of Petronas Yamaha’s Morbidelli, who a week earlier beat the Aussie to the chequered flag in a thrilling finish at Valencia.
Appearing in his final race with the Pramac Ducati team, Miller continued his impressive late-season form after starting from second on the grid in Portimao.
Miller stalked the Italian until the final lap, making a quick strike in the dying stages to secure second place.
“Miguel was on another level today. I was trying to manage the race at the beginning and I thought especially in the first laps he went away so quickly from us,” Miller said.
“Franky (Morbidelli) and I were running a really good pace and he (Oliveira) was still gapping us.
“I just did the maximum I could do today; it was kind of hard to pass, harder than I expected around here.
“I wanted to make the move a little bit earlier on Franky, then I got a bit close because one corner leads into another and you’re braking on the angles. I felt like I got a little bit too close so I had to run wide.
“I was playing a game of yo-yo, but I managed to make it stick on the last lap this time, really happy and a massive congratulations to Miguel, seems fitting to end the season like that – it’s awesome to see.
“We’ll come back next year stronger, I’ve really found my groove in the last few (races) with the bike, I’m feeling good coming towards next year.”
Miller’s second-place finish helped Ducati secure its first manufacturers’ title since 2007 ahead of Suzuki, who had a tough weekend with new MotoGP™ champion Joan Mir forced to retire and Alex Rins in P15.
An exciting move to the factory Ducati Team awaits Miller, who will set his sights on challenging for the World Championship in 2021.