Cristiano Ronaldo's Portugal and 2010 winners Spain progressed from Group B in dramatic fashion on Monday, joining host nation Russia and Uruguay in the next stage but technology grabbed centre stage.
Spain, who will play the Russia in Moscow on Sunday, ended up topping Group B by virtue of goals scored but only after an inju
ry-time strike by Iago Aspas -- confirmed by the video assistant referee -- ensured a 2-2 draw.
In Saransk, Ronaldo was at the heart of a series of VAR incidents. First he had a penalty saved by Ali Beiranvand and was later saved by a review as Iran's players called for him to be sent off following an incident with Morteza Pouraliganji.
Iran coach Carlos Queiroz said Portugal captain Ronaldo, who will line up against Uruguay in the next round, should have been sent off for using an elbow in the 1-1 draw.
"I don't want to talk too much, it's about my country and a player. I know it'll be a war against me," said Queiroz, who coached his native Portugal at the 2010 finals in South Africa.
"But the reality is you stopped the game for VAR (video assistant referee), there is an elbow," he added. "An elbow is a red card in the rules. In the rules it doesn't say if it is (Lionel) Messi or Ronaldo."
Portugal will face two-time winners Uruguay in Sochi on Saturday.
Argentina will look to join Spain, Portugal, Russia and Uruguay in the next round but must rely on the outcome of the other match in Group D.
Held to a draw by tiny Iceland -- with Messi missing a penalty -- and humbled by Croatia, Jorge Sampaoli's men could already be packing their bags.
The maths is simple: if Argentina beat Nigeria and Iceland fail to win against Group D leaders Croatia, they will go through to the last 16. If Iceland win, it will be time to get the calculators out.
Argentina's struggles in Russia come after their pre-tournament preparations were wrecked by controversy and poor form, coupled with a reliance on a top-heavy, limited squad.
The Argentine federation was even moved to confirm that coach Jorge Sampaoli would continue for the final group game amid rumours of a rift between players and coach.
"We have to make our goal five games to reach the final. Tomorrow will be the first final," said the defiant coach on the eve of the game in Saint Petersburg.
"No matter who plays tomorrow will have the obligation to give until the last bead of sweat so that Argentina will go through."
Euro 2016 heroes Iceland can still dream of progress to the knockout rounds but they must beat Croatia and hope the other result goes their way.
Elsewhere on Tuesday, 1998 champions France take on Denmark in Moscow with top spot in Group C up for grabs.
Denmark require just a point to join France in the knockout stages, and could even pip Les Bleus to top spot with a victory.
"We are not going to give them a helping hand. Our goal is to guarantee first place and two results will allow that," Deschamps said.
"I would never say to my team that we're playing for a draw. I want my team to go out onto the pitch without any ambiguity and to do everything to win this match."
Australia still have a slim chance of progressing if they beat Peru heavily and Denmark lose to France.
Russia were buoyed by huge support in their first two matches, sweeping aside Saudi Arabia and Egypt, but the wheels came off against Uruguay in a chastening 3-0 defeat, in which they were reduced to 10 men.
Disappointed Russian coach Stanislav Cherchesov said it was better to lose heavily now than in future games but added: "Psychologically we are well prepared for the next games."
Two-time winners Uruguay, with Luis Suarez and Edinson Cavani on the scoresheet, pipped Russia to top spot in Group A.