The Dragons pulled off an emphatic victory as Leinster's unbeaten run came crashing to and end at Rodney Parade. Gareth Wyatt scored twice in the first half to send the Dragons on their way before Gareth Cooper and Kevin Morgan wrapped up the bonus point for a convincing win.
For Leinster, Shane Horgan had put them ahead after only 11 minutes, but not even the return of Brian O'Driscoll and the rest of their international stars could inspire much response to the Dragons fire.
Wyatt went over inside three minutes after Sweeney's long pass to Morgan caught the visitor's defence out-manned. The fleet -footed wing slid over in the corner inside three minutes despite Gary Brown's covering tackle.
After Horgan had latched onto O'Driscoll's hack ahead to take the lead, Wyatt then pounced on some hesitant defending from Morgan's speculative kick to regain the lead from the home side.
Filipe Contepomi kept Leinster within touching distance for more than an hour but despite an edge in the scrums, Kidney's side failed to hold onto the ball long enough to build any momentum and faded badly as the game wore on.
Sweeney booted two crucial penalties to open day-light between the sides before Cooper and then Morgan wrapped up the game. Cooper finished a scorching break by Wyatt after Michael Owen's neat inside pass and then Morgan rounded Horgan in injury time to clinch the bonus point and cap a memorable night for the Dragons.
Dragons: K Morgan; G Wyatt, P Montgomery, S Tuipolotu, N Brew; C Sweeney, G Cooper; R Snow (A Black, 57), S Jones (J Richards, 69), R Thomas (C Anthony, 64), I Gough, P Sidoli, R Bryan, M Owen (capt), J Ringer
Tries - G Wyatt (2), G Cooper, K Morgan. Con - C Sweeney. Pens - C Sweeney (4)
Leinster: D Hickie; S Horgan, B O'Driscoll (D Quinlan, 73), C Warner, G Brown; P Contepomi (K Lewis, 73), G Easterby (B O'Meara, 73); R Corrigan (capt), S Byrne (G Hickie, 73), R Nebbett (P Coyle, 73), M O'Kelly (D Dillon, 73), B Gissing, E Miller, V Costello, S Jennings
Try - S Horgan. Con - P Contepomi. Pens - P Contepomi (2)
Referee: R Dickson (Scotland)