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Wales were stunned by a 20-point salvo from Ireland in the opening 28 minutes that brought converted tries for wing Simon Zebo and prop Cian Healy.
Returning former Ireland captain Brian O'Driscoll went over from a metre out, his 46th international try in 121 matches, early in the second half and although Wales countered with scores from Alex Cuthbert, Leigh Halfpenny and Craig Mitchell, their stirring fightback fell short.
No side has won back to back grand slams since France in the old Five Nations in 1997 and 1998.
Ireland had lost their last three to Wales, including the 2011 World Cup quarter-final, and set out energised and with a steely determination to atone.
The men in green struck with an opening try after 10 minutes, punching a hole in the Welsh backline first from a swift attack that was only halted when right wing Craig Gilroy ran out of space.
The Irish won a lineout after a knock-on and from quick handling, O'Driscoll's run took the attention of three defenders before the centre, who has hardly played since the World Cup because of injury, fed Zebo to scamper over.
Desperate Welsh defence on their own line prevented another try - Ireland settling for a penalty from Jonny Sexton - but they soon threatened again.
With stony-faced coach Warren Gatland, now seconded to British and Irish Lions duty, looking on from the stands, the howls of derision from a stunned Millennium stadium crowd grew louder still when Dan Biggar's clearance was charged down and caught by hooker Rory Best.
Ireland had numbers in support although it took some fine footballing skills from Zebo to flick up a pass behind him with his left heel before gathering to maintain an attack fnished off by Healy.
Wales, low on confidence and dazed by Ireland's aggressive running, finally got on the board with Leigh Halfpenny's penalty and despite getting up a head of steam late in the half, their first persistent spell of pressure ended when they were penalised close to the Irish try line.
Another sloppy start led to a turnover and O'Driscoll's score from close range soon after the restart.
Wing Alex Cuthbert stemmed the tide by bursting through to touch down and after Best was sin-binned, Halfpenny's try in the corner kickstarted a spell of relentless pressure.
Ireland, reduced to 14 again with scrumhalf Conor Murray shown yellow, buckled and bent in the last 20 minutes in the face of a Welsh onslaught.
Replacement Craig Mitchell barrelled over for another try but Ireland were by then home and dry.
O'Driscoll, who is seeking selection for a fourth Lions tour this year, was named man-of-the-match.
"We started really well, we came out of the blocks in the first half and played really well," he told BBC television.
"In fairness they were not going to be flat for the whole game and they really put it to us in the second half. They built momentum and if you can build IT it's hard to stop it."