19:00 BST, Tuesday 26th June, Rostov Arena (Rostov-on-Don, Russia), BBC Two
Touted as the group of mystery pre-tournament, it's become exactly that as Nigeria's 2-0 victory over Iceland has left any one of three nations in with a chance of qualifying for the last-16.
Following two wins and two clean sheets over Nigeria and Argentina, Croatia sit pretty at the top of Group D with nothing left to worry about other than winning all three of their group games, whilst Iceland are left with their dreams in tatters with one point from two games.
A win is an absolute necessity - coupled with a draw in Nigeria and Argentina's game - and a comfortable one at that, as Argentina can still qualify should they beat the Super Eagles.
Come Tuesday, the mystery will be solved.
Last Time Out
Nigeria 2-0 Iceland
World Cup debutants Iceland saw their chances of qualifying for the last-16 fade away as Ahmed Musa scored both goals for the Super Eagles to kick-start their own campaign in Group D. Nigeria would have been eliminated had they lost, but came up trumps when it counted.
Read five things we learned from Iceland's defeat HERE.
The Super Eagles would have joined Egypt and Morocco on the early flight out of Russia had they lost, and they started slowly, failing to have a shot at all in the first half.
Iceland capitalised on Nigeria's hesitancy, with Gylfi Sigurdsson forcing two saves from 19-year-old Francis Uzoho, but they faded as the game wore on.
Musa converted Victor Moses' cross on the half-volley to open the scoring, before rounding Hannes Halldorsson to make it two, whilst Sigurdsson put a VAR-awarded penalty over the bar in the 80th minute to compound their misery.
Argentina 0-3 Croatia
La Albiceleste watched their dreams crumble before their eyes as a dominant Croatia side inflicted on them their heaviest World Cup defeat in sixty years.
In truth, Argentina were the better of the two sides in the early exchanges and Croatia struggled to create clear-cut opportunities, but an error from Willy Caballero completely changed the complexion of the game.
Trying to chip the ball over Ante Rebic from a back-pass, the Chelsea backup blundered in his efforts, with Rebic volleying the botched clearance into the goal. In fairness, the Eintracht Frankfurt forward did extremely well to hit that so perfectly.
Read more on Croatia's chances in the latter stages of the World Cup HERE.
Heads dropped significantly and Argentina proceeded to collapse as Croatia took control of the game.
Captain Luka Modric doubled their lead with a sumptuous curling effort, before Ivan Rakitic added gloss to the victory with a tap-in in injury time at the end of the game as Croatia sealed their spot in the knockout rounds.
Johann Berg Gudmundsson is expected to return after missing out through injury against Nigeria, whilst Emil Hallfredsson is expected to come back into the starting XI to allow Gylfi Sigurdsson to take a more advanced position.
The 4-4-2 clearly did not work last time out, so Hallgrimsson will revert back to the 4-5-1 that earned them a point in their opener. This means that Jon Dadi Bodvarsson will miss out.
With a place in the last-16 now secure, Zlatko Dalic could use this as an opportunity to rest some players, with the likes of Andrej Kramaric, Marko Pjaca and Mateo Kovacic coming into the starting XI.
Key Battle: Aron Gunnarsson (Iceland) vs Mateo Kovacic (Croatia)
Dalic will be well aware of Iceland's strengths, that being their ability to dig deep and defend in a low block, breaking up play in the middle third of the pitch and launching counterattacks through Gylfi Sigurdsson.
Essential to their ability to do so is Cardiff City's Aron Gunnarsson. The central midfielder has been a key figure of Iceland's rise in international stature and he's, thus far, had an impressive World Cup in the middle of the pitch.
KEY STAT: Aron Gunnarsson won three tackles in Iceland's 2-0 defeat to Nigeria.
Dalic, therefore, will need to deploy a midfield capable of retaining the ball and building play. In Mateo Kovacic, Croatia have one of the best ball retainers in the world. The Real Madrid midfielder is known was for his press resistance, as well as his strength in possession and ability to progress the ball.
Kovacic will be crucial in Croatia's attempt to retain the ball in midfield and play through Gunnarsson.
Who needs what?
Iceland looked in fine fettle after their opening game draw against Argentina and - following a disappointing performance from Nigeria against Croatia - many tipped the debutants for a spot in the last-16.
However, they have a mammoth task on their hands following defeat to the Super Eagles. Iceland now need to beat Croatia and hope Nigeria don't win against Argentina.
Goal difference will be important, though, and Iceland need a resounding result to ensure a safe passage into the next round. With their future now out of their hands, Iceland's journey is likely over.
Abandoning what they know
Iceland have made a name for themselves as a defensively sound nation since their victory over England at the 2016 European Championships, and it's how they earned a point against Argentina in their World Cup opener.
However, with a win now a necessity, it could mean manager Heimir Hallgrimsson abandons his previous tactics in favour of something more expansive.
It's no use keeping ten men behind the ball without an outlet for a counter-attack when it's a matter of all or nothing.
Simply, Iceland have to go for it.
However, this will leave them particularly vulnerable at the back, made worse after centre back Ragnar Sigurdsson was taken off against Nigeria. Visionaries Luka Modric and Ivan Rakitic could have a field day against an exposed Iceland back four.
Prediction: Iceland 1-2 Croatia
Despite topping a qualifying group containing Croatia - as well as beating them with a 90th minute winner along the way - this is a different side to the one Iceland faced previously.
Croatia are in tournament mode and they seem focussed and determined to at least match their best-ever finish at the World Cup - third in 1998. An impressive victory over Argentina turned some heads, and it's just a matter of professionally tying up the loose ends against Iceland.
Listen to the RealSport football writers discuss all the action from Day 8 of the World Cup in Kremlins in the Basement: RealSport’s daily World Cup podcast.