World Cup 2018: The key moments that have the biggest teams thinking "what if?"

Reuters/SERGIO PEREZ

It feels like a lifetime ago already, but just a couple of short weeks ago the groups concluded and had people stunned at the way the routes to the final panned out. On one side, you had several of the tournament favourites and heavyweights of international football: Brazil, France, Belgium, Uruguay, Cristiano Ronaldo's Portugal and Lionel Messi's Argentina. 

The other looked a miraculous opportunity. Nobody had predicted that any of England, Croatia, Denmark, Russia, Sweden would go deep into the tournament. They barely had a quarter-final between them over the last decade in either the Euros or a World Cup. Colombia fared well at the last World Cup but had their talisman James Rodriguez missing going into the knockouts.

Spain as pre-tournament favourites stood out but looked off-colour in stodgy performances against Iran and Morocco in the group stage. When they didn't shake it off and exited meekly at the hands of the hosts, it was confirmed something special would be happening: the stars had aligned to allow an outsider into the final for the first time since Czechoslovakia in 1962. 

In the end, it was to be Croatia lining up at the Luzhniki Stadium for the final, and deservedly so: coming from behind to take all three knockout games into extra time and progress each time, the experience and pedigree of Champions League winners Mario Mandzukic, Ivan Rakitic, and Luka Modric were vital components of their run. 

But there will be teams, some of whom were sent home long ago, that will look at Croatia and think how it might have been them. 

Here are the key moments that will give fans sleepless nights: