It was the first time since 1985 that Ireland had beaten all the other home nations - England, Wales and Scotland - in a single Six Nations season. But defeat for Scotland meant they collected the wooden spoon after losing all four of their matches.
However, their vastly improved display ended Ireland's slim hopes of winning the Championship - they needed to win here by 50 points - ahead of Saturday's final match in Paris between England and Grand-Slam chasing France.
As well as centre D'Arcy's double, Ireland also scored tries through Geordan Murphy, Peter Stringer and David Wallace with Ronan O'Gara kicking 12 points. Scotland managed a try through flanker Allister Hogg, captain Chris Paterson and fly-half Dan Parks booting over their other scores.
Ireland, for all their territorial and possesion dominance, were made to sweat in the first half by a Scotland side all but written off following their 31-0 thrashing by France last time out. Indeed it was the visitors who took the lead when full-back Paterson landed a penalty in the opening minute after Ireland infringed. However, Ireland fly-half O'Gara responded in kind soon afterwards to make it 3-3.
Ireland's forwards were starting to create space for their dangerous backs but Scotland were hanging on and were helped by O'Gara's ninth minute penalty miss - the first of several goalkicking errors in the opening 40 minutes. But O'Gara's off-day with the boot was put to one side when Ireland scored the game's first try with a flowing move in the 18th minute.
Ireland captain Brian O'Driscoll, in his 50th Test, split the Scottish defence with a huge pass out to wing Shane Horgan. He in turn switched play inside to the onrushing D'Arcy who burst past Paterson and wing Simon Danielli for his first Ireland try in his 10th Test. O'Gara pulled the conversion but, at 8-3, Ireland were in charge.
Scotland though kept pressing and another Paterson penalty reduced the gap to 8-6 in the 23rd minute before seeing another effort bounce back off the post after O'Gara found his range to take Ireland to 11 points. Scotland deserved that penalty but Paterson was booed after wing Simon Webster trampled on O'Driscoll's head in the build-up.
Fly-half Dan Parks then put Scotland just two points behind with an opportunist drop goal from 40 metres. But Ireland had the last word of the half with a second sweeping try. From a scrum, scrum-half Peter Stringer found centre O'Driscoll and his pass out wide found left wing Geordan Murphy who dived over for a try. O'Gara missed the conversion but Ireland were 16-9 ahead.
Scotland coach Matt Williams, formerly in charge of Irish province Leinster, replaced prop Allan Jacobsen with Gavin Kerr at half-time. And soon afterwards they lost back-row Simon Taylor with what looked like a knee injury. Scotland though were unbowed spending several minutes encamped on the Ireland line and were rewarded when flanker Allister Hogg dived over from close range.
Paterson converted and Ireland, 1/20 favourites found themselves all square at 16-16 in the 48th minute. But nerves were settled soon afterwards when, following a lineout, flanker David Wallace was driven over for a try. This time O'Gara converted and Ireland were 23-16 ahead. Ireland though could not stop Scotland launching another marauding raid and it needed a brilliant cover-tackle by O'Driscoll on lock Stuart Grimes to prevent a try.
It was a different story though at the other end. Scotland's defence had been their Achilles heel all season and it proved to be again when after a solid drive by his pack, Stringer sneaked over from close range for a 62nd minute try. O'Gara converted and Ireland were 30-16 up.
And D'Arcy then set the seal on a memorable day in the 74th minute with a mazey run that saw him swap passes with Murphy before crossing for a second try.
AFP - 2004.