The Leinster skipper booted 23 points from seven penalties and converted Girvan Dempsey’s injury-time try as the Dragons were denied in their third consecutive away game.
Despite the loss of Craig Warlow before kick-off due to illness on the flight over, the visitors began brightly. Wales under-21 international Aled Thomas stepped in at fly-half and through the enterprise of Sione Tuipulotu, they nabbed an early converted try.
Burly Tongan Tuipulotu won the race to his own chip kick outside the home 22, flicking the bouncing ball to Hal Luscombe and his inside pass saw Leigh Hinton dart over to score and convert.
Leinster’s new-look pack was being bossed off the ball but, fortunately for the Irishmen, Contepomi’s kicking was again accurate. Two sweet penalties from the Argentinian saw Leinster claw back before the half-hour.
A third Contepomi effort pushed Leinster in front before their first fluid attack saw Ireland under-19 captain Kearney, from 40 metres out, go past Rhys Thomas and step inside Dragons captain Kevin Morgan for a scintillating 39th-minute try.
The teenager’s third try in three outings went unconverted at 14-7 but Hinton smacked a penalty off an upright and drew another late kick wide to let Leinster off the hook Playing their game second in four days, Paul Turner’s Dragons predictably tired and the 51st-minute sin-binning of flanker Andrew Hall allowed Contepomi to kick Leinster 10 points in front.
A silly deliberate offside from Kearney saw the youngster yellow-carded and that allowed the Dragons back into it. Just past the hour, Contepomi landed his fifth penalty but that was soon
cancelled out as a 71st-minute kick through from Gareth Baber squirmed away from Kearney, allowing Luscombe in for a try.
Hinton converted to put the Dragons within a converted score but the prospect of even a bonus point was soon gone as Contepomi chalked up two more penalties.
Tuipulotu’s injury-time sin-binning for hands in the ruck was followed by Dempsey’s try at the death on a night when Lions Shane Horgan and Denis Hickie both came off the bench.