Rea had dominated the weekend with wins in Race 1 and the Superpole - he has not failed to win on the Losail track since 2016 - and got the better launch down to Turn 1, but his great rival Alvaro Bautista went as late on the brakes as he could.
The Spaniard was momentarily ahead but ran wide and allowed the five-time world champion to re-take the lead on exit.
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Second time around, Bautista's Ducati had him ahead before they even reached the corner, such was the overspeed in a straight line.
However, Rea is not more than 100 points clear in the standings for no reason and he was back ahead inside a minute while Bautista desperately scrapped to get ahead.
The pair had won 16 races each going into the final battle of the season and pride was very much at stake between the two but Bautista's scrappiness saw him fall into the clutches of Alex Lowes.
He was able to repel the Englishman but Rea was too quick through the corners for his opponent to make any move stick and his team-mate Chaz Davies was the beneficiary, taking second place with five laps to go.
The Ducati squabble allowed Rea the opportunity to disappear up the road and by the time the chequered flag was waved on 2019, he was fittingly more than three seconds clear.
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