The Irish have prevailed in the last 15 meetings between the Pool C rivals dating back to 1997 and are strong favourites to claim the win they need to reach the quarter-finals.
But this year's Six Nations issued a timely reminder that the Azzurri remain a threat after only a late Ronan O'Gara drop-goal prevented a first defeat to the Italians in the competition.
"Everybody in the Irish camp realises we didn't deserve to win that Six Nations game, but we did and these things happen," said Jennings.
"It was a pretty even game. We set ourselves up for that drop-goal at the end.
"I don't know really why it happened but we underperformed that day.
"We knew what we were heading into. It's always very difficult in Rome.
"If you give them ball like we did that day, they can do damage and it was a very even game. We're expecting the same this weekend."
Defeat will almost certainly see Ireland depart the World Cup, though if they were to lose while securing two bonus points they would be reprieved.
The scene is set for a fascinating encounter that Jennings insists his side are quietly confident will bridge their path into the knockout stages.
"There will be no complacency. We're very realistic, certainly not over-confident, but we know we have the ability to win," said the Leinster openside.
"You have to back up the words with a performance and we realise we are up against a very experienced team with some quality players and good leaders.
"The obvious thing that comes out every time you play Italy is that they've very physical and can match that with some dangerous runners."
Italy secured a try-scoring bonus point in their 27-10 triumph over the United States on Tuesday to set up the shootout for a place in the quarter-finals.
After the match, Azzurri coach Nick Mallett threw down the gauntlet to Declan Kidney's side by promising them a torrid time in the scrum.
"Ireland are a great side and played very well against Australia," said Mallett.
"They dominated Australia physically but we know perfectly well that we've got a better front row than Ireland, and we're going to go in there to prove that on Sunday."
Jennings understands the thinking behind Mallett's claim as the sides prepare for what should be a ferocious battle at the scrum.
"Their coach is backing his players and they are a quality front row, so he's not far wrong," he said.
"They are good players, have a strong scrum and have done a lot of damage. We know we can match them, though."
Rob Kearney (bruised knee), Keith Earls (bruised leg), Sean O'Brien (bruised arm), Tommy Bowe (calf) and Paul O'Connell (hamstring) and Gordon D'Arcy are continuing their rehabilitation from injury, though none have been ruled out against Italy.
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