Ireland will almost certainly be dumped out of the World Cup if they lose Sunday's final group game against Italy at Otago Stadium.
The Azzurri claimed a crucial try-scoring bonus point in their 27-10 victory over the United States, leaving them just three points behind Pool C leaders Ireland.
Even if the Irish were to claim a losing bonus point on Sunday, Italy would still progress to the quarter-finals on the head-to-head rule.
The only way Ireland can lose the match and still reach the knockout phase if they were to secure try-scoring and losing bonus points, while hoping Italy fail to score four tries.
It is quirk of the group that the Irish could defeat the World Cup's second favourites Australia and finish with three victories from four games, yet still be forced to return home on Monday.
The permutations have turned the final match of the tournament's pool stage into a straight shoot-out for a place in the last eight.
Ireland, who have amassed 15 successive victories over Italy dating back to 1997, will start as heavy favourites.
However, only a late drop-goal from Ronan O'Gara prevented the Azzurri from registering a first RBS 6 Nations victory over their rivals in February as they slipped to a 13-11 loss.
Italy have targeted a place in the quarter-finals and have always viewed success against Ireland as their ticket out of Pool C.
Counting against them, however, is the fact they will be playing their second game in six days with the USA having proved energy-sapping opposition.
Italy coach Nick Mallett, speaking after the Eagles had been dispatched, believes his side's scrum gives them a fighting chance in Dunedin.
"We know perfectly well we have a better front row than Ireland and we're hoping to prove that on Saturday," said Mallett. "If our front row put us on the front foot, we can win the game."
Australia should finish on 15 points if, as expected, they secure a bonus-point victory over Russia on Saturday.