South Sydney produced their best when it mattered least on Saturday night with a 41-6 annihilation of St George-Illawarra that sent the NRL ladder leaders crashing to their third successive defeat.

The Rabbitohs' finals chances may be dead and buried but they totally dominated the Dragons, sending the title favourites crashing to their heaviest defeat of 2009 to raise serious questions about their premiership credentials.

The Dragons simply didn't execute in attack while their defence was abysmal, conceding seven tries as John Sutton, Chris Sandow and Issac Luke ran riot in front of 19,918 fans.

It was the most points the Dragons had leaked all year, but the manner in which Souths cut through their woeful defence will worry master coach Wayne Bennett with his side in a slump on the eve of the finals.

Three South Sydney players scored untouched while the other four tries came as defenders simply fell off regulation tackles close to the tryline.

Sutton finished with a double while Colin Best (18th minute), Ben Lowe (29th), Jamie Simpson (57th), Nathan Merritt (59th) and Eddy Pettybourne (71st) all joined in the riot to embarrass the Dragons.

The Dragons only points came in the 23rd minute when Jamie Soward completed a midfield break by Beau Scott.

They crossed the stripe twice in five minutes earlier in the first half, but winger Brett Morris's left foot slid out and centre Matt Cooper dropped the ball over the line - both the result of committed defence.

Souths halfback Sandow gave his side a 19-6 lead at halftime with a cheeky 18m field goal in the final 20 seconds of the first half.

The Rabbitohs put the result to bed with three tries in nine minutes midway through the second half to secure their first win after successive losses had ended their finals hopes.

The loss opens the door for the Bulldogs to snatch the minor premiership off the Dragons and also leaves the red and whites' top-two position under threat ahead of Friday's clash with red-hot Parramatta.