Ireland internationals Shane Horgan and Brian O'Driscoll played starring roles as Leinster secured the provincial bragging rights with a 31-16 victory over Connacht in the Magners League at a packed-out Sportsground.
The westerners' fly-half Mark McHugh was heralded as a hero last week when he landed an injury-time penalty to steal a 22-22 draw against Edinburgh, but the Dubliner turned villain as his errors directly resulted in two Leinster tries.
Connacht came into the game having not beaten their eastern rivals for two and a half years and it looked like nothing would change when, just 30 seconds in, giant lock Trevor Hogan charged over for a try after charging down a McHugh kick.
But with Argentinian number 10 Felipe Contepomi off form with the boot - he missed three kicks at the posts in the first half - Connacht scrapped and stayed in touch.
There were flashes of brilliance from the returning internationals. Looking refreshed after the Ireland squad's 10-week conditioning programme, both Horgan and captain Brian O'Driscoll were prominent in broken play.
Following a successful Contepomi penalty and despite losing Australian scrum-half Chris Whitaker to a shoulder injury, Leinster had moved 13-0 clear by the 32nd minute.
O'Driscoll flicked a beautiful pass behind his back to the supporting Jamie Heaslip who offloaded for Guy Easterby, Whitaker's replacement, to dot down.
Nonetheless, Connacht cut the gap to six at 13-7 by the break as Matt Mostyn combined with Galway-born full-back Daniel Riordan, who ran an excellent line, to send centre Darren Yapp in under the posts. McHugh added the easy conversion.
McHugh kicked two penalties to a single Contepomi effort during a dull third quarter.
Both McHugh and Leinster prop Ronan McCormack were yellow-carded just after the hour mark for scuffling.
Malcolm O'Kelly, fresh from the Leinster bench, joined them just minutes later as the Ireland lock was found guilty of killing the ball as Connacht pressed for a try.
With a man advantage, Michael Bradley's hosts quickly drew level at 16-16 thanks to Riordan's penalty, but some lacklustre defending saw them falter in front of their biggest crowd of the season.
Gordon D'Arcy nudged Leinster ahead again with a drop goal, seven minutes from the end, and Horgan and Denis Hickie, who cruelly intercepted McHugh in midfield, both waltzed over in injury time to add some much-needed life to Leinster's title bid.
Italy Under-20s held off a late Samoa blitz to retain their place in the World Rugby U20 Championship on Saturday and head coach Alessandro Troncon believes the experience will have served as a valuable lesson for his young troops.