One side will progress to the final, while the other must miss out on yet another World Cup, as Northern Ireland travel to Italy for their European playoff semi-final on Thursday evening.
The winner of a high-stakes clash in Bergamo will then visit either Wales or Bosnia-Herzegovina, with a place in this year's global finals up for grabs.
Match preview
Italy may be four-time world champions - most recently two decades ago - but despite winning the delayed Euros in 2021, they last trod the global stage some seven years earlier.
This is their third consecutive World Cup qualifying campaign to end with a place in the playoffs, following painful defeats to Sweden and North Macedonia.
Last September, the Azzurri started Group I with a 3-0 away loss to Norway, which forced former coach Luciano Spalletti to depart; under new boss Gennaro Gattuso, they posted six straight wins before facing the Norwegians again.
Requiring a huge margin of victory to seize top spot - and, with it, direct qualification - Gattuso's side instead finished with another dispiriting defeat, as Erling Haaland struck twice in a stunning away win.
Citing the crowd's angry reaction to that 4-1 reverse in Milan, 2006 World Cup winner Gattuso asked to play this week's game in nearby Bergamo, rather than at his old home ground of San Siro.
Reasoning that a more compact stadium could work in Italy's favour, he must now lead La Nazionale into a nerve-shredding playoff decider by beating Northern Ireland.
Aiming to avoid becoming the first former winners to miss out on three successive World Cups, the Azzurri now meet opponents they last lost to back in 1958.
The sides most recently met five years ago, when a 0-0 draw at Windsor Park denied Italy automatic qualification for Qatar 2022 and led to the infamous 'disastro' against North Macedonia.
While Northern Ireland fought hard for that result in Belfast, they have lost on all seven previous visits to Italy by an aggregate score of 16-2, failing to find the net on six occasions.
In fact, they last scored against the Azzurri anywhere in a 1961 friendly, so history will be stacked high against the away side on Thursday evening.
Ultimately seeking a first World Cup finals appearance for 40 years, Northern Ireland did come close to reaching Russia 2018 but lost 1-0 on aggregate to Switzerland in the playoffs.
This time, they must succeed on Italian soil, then beat Wales or Bosnia in order to join co-hosts Canada, Switzerland and Qatar in Group B.
Though they only finished third in Group A of European qualifying, being beaten both home and away by Germany, NI qualified for these playoffs by virtue of their UEFA Nations League performance.
A decade on from their spirited showing at Euro 2016, Michael O'Neill is back in charge - alongside his club role at Blackburn Rovers - and aims to take a young squad all the way to North America.
However, Northern Ireland's last three competitive away wins were against minnows Lithuania, San Marino and Luxembourg, while they have lost their last six trips to teams ranked inside FIFA's global top 20.
Italy World Cup Qualifying - Europe form:
W W W W W L
Northern Ireland World Cup Qualifying - Europe form:
W L W L L W
Team News
Coming amid a hectic phase of the club season, Italy have several injury issues to deal with for this playoff semi-final.
At the back, Napoli captain Giovanni Di Lorenzo is absent, while Alessandro Bastoni and Gianluca Mancini are both carrying knocks, but Riccardo Calafiori has been cleared to play after suffering a minor problem in Sunday's EFL Cup final.
Up front, Atalanta striker Gianluca Scamacca is struggling with an adductor issue and Liverpool's Federico Chiesa has already withdrawn; the latter was replaced by Bologna winger Nicolo Cambiaghi.
So, Mateo Retegui, Moise Kean and in-form Francesco Pio Esposito are all vying for selection. The latter has scored three times in his last four World Cup qualifiers and has recently netted Inter Milan's last two league goals.
Newcastle United midfielder Sandro Tonali will have his fitness monitored; Northern Ireland's Dan Ballard also missed the recent Tyne-Wear derby and must sit out this crucial clash with a hamstring injury.
Tom Atcheson - who plays under O'Neill for Blackburn - has been called up from the Under-21s as cover, but any two of Ruairi McConville, Ciaron Brown and Eoin Toal are more likely to start alongside Paddy McNair in central defence.
George Saville missed the last qualifier against Luxembourg due to suspension but is now back in the fold, along with fit-again pair Shea Charles and Ali McCann, plus goalkeeper Pierce Charles.
However, the visitors will be without two influential full-backs: captain Conor Bradley and the experienced Jamal Lewis.
Italy possible starting lineup:
Donnarumma; Calafiori, Mancini, Bastoni; Cambiaso, Tonali, Locatelli, Barella, Dimarco; Kean, Retegui
Northern Ireland possible starting lineup:
P. Charles; Hume, McConville, Brown, McNair, Devenny; Saville, S. Charles, McCann; Price, Reid
We say: Italy 3-1 Northern Ireland
Italy have only lost two home World Cup qualifiers dating back to 1934, but given their playoff history, nerves will be jangling until they make a breakthrough in Bergamo.
While Northern Ireland have an improving young team, the Azzurri have found their shooting boots under Gattuso, and such firepower should see them into next week's decider.
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