Ireland booked their place in the World Cup quarter-finals as Keith Earls' first-half try helped Joe Schmidt's side to a 16-9 win over Italy.
Earls' score at the Olympic Stadium was his eighth in World Cups, making him Ireland's top try-scorer in the history of the tournament, while fly-half Johnny Sexton kicked 11 points to hold off a spirited Italy.
Ireland are guaranteed to reach the knock-out stages and will play France next Sunday to decide who finishes top and likely avoids champions New Zealand in the last eight.
Defeat ends Italy's chances of progress but Jacques Brunel's side can take heart from a determined performance, which stretched a team many believe represent Europe's best hope of becoming champions.
Ireland knew victory against Italy would send them back to the top of Pool D and seal their place in the World Cup quarterfinals.
Joe Schmidt made 11 changes to the rotated side that thrashed Romania but Simon Zebo, Keith Earls and Tommy Bowe retained their spots, with Jared Payne out with a bruised foot and Rob Kearney still recovering from a hip injury.
Italy, needing to win to avoid elimination, risked talismanic No.8 Sergio Parisse, who had missed their opening two matches with a calf haematoma.
Parisse had to have his calf drained in order to be fit for the clash at the Olympic Stadium and, with his leg heavily strapped, the 32-year-old showed signs of rustiness early on when he spilled a simple pass.
After a nervy start, Ireland seized the initiative as Johnny Sexton made a darting break forward and while Italy staved off the try, an offside allowed Sexton to kick his side into a 3-0 lead.
It was Italy, however, who were enjoying the majority of possession and after a breakdown infringement from Jamie Heaslip, fly-half Tommaso Allan slotted the penalty to draw level.
Under pressure, Ireland again sprang into life as Sexton played an inside pass to Robbie Henshaw, whose quick offload put Keith Earls over the line for the opening try, which Sexton converted for a 10-3 lead.
Earls' try was his eighth at World Cups, taking the 28-year-old ahead of Brian O'Driscoll as Ireland's top try-scorer in the history of the tournament.
Italy reduced the deficit to four when Allan kicked another penalty and they felt aggrieved soon after when Quintin Geldenhuys was pulled up for a dangerous tackle on Dave Kearney, but Sexton struck the post with the long-range penalty.
Ireland swarmed forward as the game approached half-time but they failed to capitalise as Italy, led by Parisse, defended resolutely to ensure the score remained 10-6 at the interval.
The contest restarted where it had left off, with Ireland on top, but in the 49th minute, it was Italy who went closest as only a sensational covering tackle from Peter O'Mahony prevented Simone Favaro from diving inside the corner.
Ireland were suddenly struggling to establish a foothold and when an Italian maul was pulled down, Allan kicked his penalty to cut the gap to one point.
Finally, the Irish gained some forward momentum, attacking the Italian 22 with renewed purpose on the hour-mark, and while a Sexton cross-kick failed to find its target, the fly-half was more precise with two penalties soon after, kicking his side into a 16-9 lead.
Italy tried to peg back their opponents once more but substitute Carlo Canna fell short with a long-range penalty before Ireland's O'Mahony was handed a yellow card for shoulder-charging a ruck.
Down to 14, Ireland looked nervous in the game's final minutes as Sexton skewed a fairly straight-forward penalty wide and Italy piled forward in search of the match-saving try.
The opening never came, however, as Ireland held on for a narrow victory and set up a thrilling pool decider with the French.
