The back-to-back NRL champions defeated Wigan Warriors in the 2019 one-off fixture and, despite falling behind against Saints on Saturday, once again came out on top against their Super League counterparts.
Luke Thompson – who will head to Australia after the season to join the Canterbury Bulldogs – opened the scoring when he crashed over from Theo Fages' pass for a converted try.
The Dragons roared back, however, with Daniel Tupou hanging on to a low pass by his boots before waltzing over the line on his side's left flank.
Joseph Manu put the visitors in front when he touched down on the opposite side of the field for his first of the game, diving over as Saints were caught short of numbers out wide.
Kyle Flanagan – making his debut for the Roosters – hit the posts with both conversion attempts, making it 8-6 at the half-time interval.
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Saints had opportunities to hit back after the break, wing Tommy Makinson ruled to have knocked on as he attempted to score under pressure.
Instead it was the Roosters who crucially scored next, Manu grabbing his second try. Luke Keary then provided the finish following Siosiua Taukeiaho's initial break from inside his own half, putting the game beyond St Helens.
Alex Walmsley did plunge over for a late consolation score, Makinson adding the extras, but Sydney held on to retain the trophy and maintain their 100 per cent record in the annual competition.
Photo: Nathan Stirk/Getty Images Caption: Sydney Roosters celebrate after their victory over St Helens.