Luke McLean makes way for Masi and drops to the replacements bench, with Giulio Tonionlatti squeezed out of the matchday squad.
Luciano Orquera, who was a try scorer against the USA, and Fabio Semenzato are the preferred options at half-back, while Salvatore Perugini, Leonardo Ghiraldini and Martin Castrogiovanni combine again in the front row.
The selected Italian panel contains 15 players who got game-time during Italy's 13-11 loss to Ireland in Rome during last season's Six Nations.
Leicester Tigers prop Castrogiovanni is the only player in the squad who does not play his club rugby in either Italy or France.
Looking forward to Sunday's game, Italy head coach Nick Mallett said: "Our whole objective for two years has been to get to this point. If we play really well, which we will have to against a very good team, we have a chance of getting to the quarter-finals.
"And there is a genuine belief that we are getting better. I remember the game (against Ireland last February) clearly because it was very, very disappointing.
"The changing room was very quiet and one of the first occasions I've seen an Italian team really, really disappointed at doing very well against another Six Nations team.
"A lot of times in the past they've been disappointed to lose, but pleased to run the opposition close. This was one of the first times there was genuine disappointment that they hadn't managed to hold out and win that game.
"That's a very good sign because it meant the team had started to believe it wasn't just good enough to be competitive, that it was really important to win tight games."
ITALY Team & Replacements (v Ireland, 2011 Rugby World Cup Pool C, Otago Stadium, Sunday, October 2, kick-off 8.30pm local time/8.30am Irish time):
15 - Andrea Masi (Aironi Rugby)
14 - Tommaso Benvenuti (Benetton Treviso)
16 - Fabio Ongaro (Aironi Rugby)
17 - Andrea Lo Cicero (Racing Metro 92)
18 - Marco Bortolami (Aironi Rugby)
19 - Paul Derbyshire (Benetton Treviso)
20 - Edoardo Gori (Benetton Treviso)
21 - Riccardo Bocchino (Estra I Cavalieri Prato)
22 - Luke McLean (Benetton Treviso)
Follow the Ireland team in New Zealand on www.twitter.com/irfurugby.