Day seven of the World Cup sees another quartet of group games played out and one of the pre-tournament favourites, Argentina, are back in action following their shock loss to Saudi Arabia.
Lionel Messi's early penalty looked like it was going to turn the game into a predictable procession but two superb goals early in the second half saw an energetic and fearless Saudi display rewarded.
Now, Argentina face perennial group stage successes Mexico in match two and it could be described as a must-win even at this early stage.
The other game in Group C sees Poland face Saudi Arabia, with the former having drawn 0-0 against Mexico first up, as Robert Lewandowski missed a crucial penalty.
Group D is also in action as defending champions France face their toughest assignment on paper against a sturdy Denmark team.
Tunisia take on Australia to complete Saturday's action, with both teams seeking their first wins of the tournament.
By some way the Saudi defeat was the biggest shock of the World Cup so far as Argentina, complete with one of the greatest players ever to play the game, completely out of ideas by the end.
In some sense, they were unfortunate to lose given the dominance of the first half where they had the ball in the back of the net four times, with three being ruled out for offside.
However, the Saudi whirlwind that ensued in the second half meant that Argentina had no real answer and a long-held 36-game unbeaten run came to an end.
Lionel Scaloni now has to find some sort of response against Mexico on Saturday and he may look to try and change things up in his ranks.
Mexico have made the last-16 in every World Cup since 1994 and they have also got some work to do to try and preserve that record.
They drew 0-0 with Poland on Tuesday in what was an underwhelming tie and they are going to have to try and find more going forward if they are to defeat the South American powerhouses.
Scaloni's men have an excellent record against Mexico with the latter's last win coming all the way back in the 2004 Copa America.
The last World Cup meeting of the two sides saw Argentina triumph 3-1 in the last-16 stage of the 2010 tournament.
Although Saudi Arabia were widely credited for their display on Tuesday, Poland will enter this match as favourites, but they will need to do more in an attacking sense to earn the win.
There weren't many chances in the Mexico game, which is why the Lewandowski penalty miss will feel all the more frustrating.
Recent form has not exactly been sparkling with just two wins from their last seven matches so Czesław Michniewicz's side will have to be wary of the threat that Saudi Arabia pose.
They will be looking to Saleh Al Shehri and Salem Al Dawsari once more after their superb goals - particularly the latter who curled his effort beyond the reach of a despairing Emi Martinez.
Much of France's build-up to the tournament was dominated by players who would not be playing and that carried on right up until the eve of the action as Karim Benzema saw his dreams crushed by injury.
However, they certainly laid down a marker against Australia on Tuesday evening, responding excellently to an early goal from the Socceroos winger Craig Goodwin.
Kylian Mbappe, who a lot of France's hopes are pinned upon, was outstanding out on the left and his frightening acceleration was too much for the Australian defence to handle at times.
Olivier Giroud, at the twilight of his career, ended a curious record of never scoring in the World Cup by getting two goals and drawing level with Thierry Henry's Les Bleus record. He will be hoping for one chance to get his 52nd for France and writing himself into the history books.
Even without the likes of Paul Pogba and N'Golo Kante, there is still plenty of talent in the side and Denmark may have to be wary.
Euro 2020 semi-finalists Denmark, tipped to be a dark horse, will have been disappointed by their 0-0 draw against Tunisia and they did not create nearly enough opportunities.
However, they didn't concede either and their run to the semis last summer was built upon being hard to break down, as was their World Cup qualification where they let in only three goals in 10 games.
Denmark won both meetings with France in the recent Nations League, while they held them to a 0-0 draw in Russia four years ago, so this one could be a very tough assignment for the reigning champions.
If either Tunisia or Australia want to get through to the last 16 then a win here is non-negotiable.
The Eagles of Carthage are playing in their sixth World Cup and they have not gone beyond the group stages in their five previous attempts.
Meanwhile, the Socceroos' only appearance in the last-16 came in 2006, before they were beaten by Italy thanks to a heartbreaking last-gasp penalty from Francesco Totti.
Both sides can be pleased with their efforts from the first game, with Tunisia holding a tough Denmark to a 0-0 draw.
4-1 may have been a harsh scoreline no Australia, particularly with their first-half performance but ultimately, Graham Arnold's men ran out of steam.
The teams have only ever met once before, in the 2005 Confederations Cup, where Tunisia won 2-0.