Replacements used: Stuart Olding (Belfast Harlequins/Ulster) for Coghlan Murray (31 mins), Tadhg Furlong (Clontarf/Leinster) for Reilly (half-time), Tadhg Beirne (Lansdowne/Leinster) for van der Flier (48), Jake Cawley (Old Belvedere/Leinster) for Furlong (59), Cathal Marsh (Dublin University/Leinster) for Farrell (61), Shane Buckley (Garryowen/Munster) for Henderson (64), Kieran Marmion (Corinthians/Connacht) for McGrath (69), Niall Scannell (Dolphin/Munster) for Conan (71).
Replacements used: Alessio Zdrilich (Ospitaletto Rugby) for Bellucci (57 mins), Pietro Ceccarelli (Stade Rochelais) for Maistri, Sami Drissi-Panico (UR Capitolina) for Bortoletti (both 61), Federico Conforti (Petrarca Padova) for Marazzi, Marcello Violi (Rugby Reggio) for Calabrese (both 62), Maistri for Scalvi, John Apperley (Rugby Reggio) for Guarducci (both 67), Giulio Bisegni (Mantovani Lazio) for Odiete (68), Luca Conti (Udine Rugby) for Zanini, Odiete for Benvenuti (both 76).
Peter Nelson, Chris Farrell and Aaron Conneely all crossed in the first eight minutes, only for Italy hit back with two tries to make it 24-12 at the break.
But second half tries from James Rael, Luke McGrath and Nelson made sure of the bonus point and a second pool victory for an Ireland team that showed nine changes to the side that lost to England.
Mike Ruddock’s charges had to wait on the result of the later South Africa-England game to determine their placing for the play-offs.
Luck was not on their side as they were knocked off top spot in Pool B by the Baby 'Boks whose four-try 28-15 win over England gave them a vital five-point return and a much-sought after semi-final berth.
Ireland finished a point behind the tournament hosts, on 10 points, and will battle it out in the middle tier - the 5th-8th place play-offs. Intriguingly, they will have a rematch with England in Cape Town on Sunday evening (kick-off 5pm local time/4pm Irish time).
There were just 58 seconds on the clock today when Nelson, slotting in at centre alongside his Dungannon and Ulster colleague Farrell, broke through for the opening try.
Ireland attacked from the kick-off with Farrell and Sam Coghlan Murray making breaks, and a surge from new out-half Jack Carty sent Rael powering through, with Nelson running the support line and his strong hand-off helped him go over untouched.
Four minutes later, Nelson was first to reach his own chip and hacked the ball through for Farrell to collect and touch down in the right corner. Carty converted in impressive fashion and Ireland wasted little time in adding to their try tally.
Good pressure from Conor Finn on kick receiver David Odiete saw the ball break free for flanker Conneely to burst past two defenders and touch down in the right corner with the accurate Carty again adding the extras.
But just as Ireland hunted for the bonus point score, a pass from McGrath in the Italian 22 was intercepted by Edoardo Padovani and he has the pace to make the line for Italy’s second try of the tournament. The try scorer calmly converted for good measure.
Suddenly, Italy were right back in the game when they punished two handling errors from the Irish. Craig Green’s youngsters attacked from a strong scrum, Finn was turned over and then Coghlan Murray was unable to gather a bouncing ball near the Irish line and scrum half Guido Calabrese pounced to score.
The unconverted try was quickly followed by a Carty penalty at the midpoint of a breathless first half, with Ireland regaining their composure but only briefly as a scrum penalty and an offside kept them pinned back in their 22.
The error count increased for both sides as half-time approached. The Italian scrum was beginning to cause Ireland problems although Padovani sent a right-sided penalty wide of the posts.
It was tit for tat when the second half got underway, but Ireland rediscovered their scoring touch to secure that all-important bonus point in the 50th minute.
Hooker Rael crashed over the right of the posts after a sustained period of pressure, with final passes from Mike Sherlock and Nelson opening up the space.
Try number five followed soon after, a solid scrum offering McGrath the chance to attack down the right and he did brilliantly to collect his well-weighted chip and step around the covering Odiete to gleefully dive over in the corner.
With eager replacements aiding an improving Irish scrum, they swooped for a sixth with 16 minutes remaining. Set piece ball was spun out to the right for the influential Nelson to notch for his second try, the centre dummying his way past Odiete with Finn supporting on his outside.
Ruddock will have wanted a tidier performance from his players - they never really matched the excellence of that opening spell - but they got the job done against a physical Italian outfit and can progress to the play-offs with plenty of confidence.
Giving his reaction afterwards, Ireland's stand-in captain Jack Conan said: "We're delighted, Italy are a big strong team and they are a good team. We came out and scored a few tries in the beginning but then deviated from the game plan but we ended strong again. The objective when we came out was to score as many points as we could, that was our game plan.
"The confidence is very high in the camp, it was a great victory against South Africa and it boosted our morale.
"We lost against England but we are back on track now against Italy. We can hold our heads high and we are confident going ahead."
TIME LINE: 1 minute - Ireland try: Peter Nelson - 5-0; conversion: Jack Carty - 7-0; 5 mins - Ireland try: Chris Farrell - 12-0; conversion: Jack Carty - 14-0; 7 mins - Ireland try: Aaron Conneely - 19-0; conversion: Jack Carty - 21-0; 12 mins - Italy try: Edoardo Padovani - 21-5; conversion: Edoardo Padovani - 21-7; 16 mins - Italy try: Guido Calabrese - 21-12; conversion: missed by Edoardo Padovani - 21-12; 20 mins - Ireland penalty: Jack Carty - 24-12; 25 mins - Italy penalty: missed by Edoardo Padovani - 24-12; Half-time - Ireland 24 Italy 12; 50 mins - Ireland try: James Rael - 29-12; conversion: missed by Jack Carty - 29-12; 54 mins - Ireland try: Luke McGrath - 34-12; conversion: Jack Carty - 36-12; 64 mins - Ireland try: Peter Nelson - 41-12; conversion: missed by Jack Carty - 41-12; Full-time - Ireland 41 Italy 12
Referee: Angus Gardner (Australia)