The Sydney Roosters have scored a double in lower grades, winning both the Jersey Flegg and Premier League Grand Finals today at Telstra Stadium.

In Premier League, the Roosters had a comfortable victory, defeating minor premiers the St George Illawarra Dragons by 30-8.

The Roosters had to overcome the early sin binning of Gavin Lester and at half time, held a handy 16-8 lead.

With the forwards getting a roll on, five eighth Luke Dorn found opportunities just wide of the ruck to extend the Roosters' lead.

For the Dragons, hooker Aaron Gorrell never stopped trying as did centre Wes Naiqama. But a solid Roosters defensive effort coupled with numerous handling errors from the Dragons saw the Roosters run out convincing winners. Gavin Lester, bagging a hat trick of tries.

Earlier in the day, after trailing 12-0, the Roosters came back to defeat the Cronulla Sharks 14-13. Red hot favourites, the Roosters kicked two field goals to the one over a gallant Sharks outfit.

The Roosters Jersey Fleggs are the first team in any grade to go through a season undefeated since 1959.