They took their time to get into their stride, but when they did, they showed more glimpses of the character and ability that inspired the upset over the Wallabies.
Their date in the quarterfinals is Six Nations rival Wales. Win that, and then beat England or France, and a team that flamed out at the last World Cup is in the final. Somcomeback.
They have backs with real zip and a loose forward trio, led by the classy Sean O'Brien, as good as any.
Ireland took control of the game by turning a three-point halftime lead into a 20-point buffer within 12 minutes of the resumption.
First five Ronan O'Gara kicked his fourth penalty of the night, before right winger Tommy Bowe created the first try.
Bowe, who looked dangerous and strong throughout, hit the line at pace and on the angle, and captain Brian O'Driscoll was on hand to score his first try of the tournament.
Then, the killer blow.
Gordon D'Arcy made a sublime break in midfield, the Irish spread the line of attack, and eventually quick ball made its way to the left flank, where winger Keith Earls was on hand to score.
O'Gara nailed the sideline conversion to quash any lingering suggestions the new covered stadium was a goal-kicker's graveyard.
It looked like becoming an Emerald Isle rout when fullback Rob Kearney bulldozed over the line shortly after, but the television official ruled he had been held up.
Predictably, the Italians did not sit back and watch their World Cup playoff hopes evaporate.
They hit back like wounded bulls, charging into rucks with vigour and accuracy and possibly just a little illegality.
But their attacks petered out, and it was the Irish who had the final say when Earls grabbed his second try out wide.
If the quality of the rugby in the first quarter had matched the intensity of the atmosphere inside Otago Stadium, a $100 ticket would have seemed an absolute bargain.
The noise levels were on a par with the opening Dunedin game, the England-Argentina epic three weeks ago.
But where that crowd was roughly split between the two teams, tonight was very much slanted in favour of the Irish.
The cheers reached ear-splitting levels when Ireland took the lead through an O'Gara penalty as the game made a testy start.
Italy replied in kind through Mirco Bergamasco, a rare goal-kicking winger. O'Gara then missed one and kicked one, before Bergamasco levelled the scores again.
Both teams were eager without quite being at their peak in terms of execution.
Ireland's backs looked likelier but Italy's forward pack looked hungrier, and it was dominating the scrum through grizzly tighthead Martin Castrogiovanni.
The Irish were convinced they had the opening try when Bowe skipped through the middle and sprinted to the line. But the juggled pass was ruled forward.
The men in green seemed to lift the tempo, and when O'Gara kicked his third penalty and the Italians lost the influential Castrogiovanni, only one side's eyes were smiling.
Bergamasco missed a late penalty that would have drawn Italy level at the break. A couple of vigorous driving mauls gave the Azzurri some renewed impetus but the clock was their enemy, and they went unrewarded for their 58 per cent share of possession in the first half.
Ireland 36 (Keith Earls 2, Brian O'Driscoll tries; Ronan O'Gara 2 cons, 4 pens, Jonathan Sexton con, pen), Italy 6 (Mirco Bergamasco 2 pens).
