If Iran can be the first team to stop Cristiano Ronaldo from scoring at this year's World Cup, the result could be historically significant. (FIFA WC 2018: FULL COVERAGE)
A final score favorable enough to move Iran into the knockout round for the first time also would carry considerable personal meaning for the Asian team's Portuguese coach, Carlos Queiroz, who was once Ronaldo's coach on their country's national team.
Queiroz, who also coached Iran at the 2014 World Cup in Brazil, called Monday's game against Portugal "the most interesting and important match in my seven years with Iran."
"People gave us no chance, but we still have chances to qualify for the second round. We'll fight for our dreams," he said. "We know it will be difficult, but as I said before, we came here and didn't expect easy things. We don't want easy things. We wish and expect to be better every single day."
Portugal, the defending European champion, is tied with Spain at the top of Group B with four points each. Iran is right behind with three, thanks to its opening 1-0 victory over Morocco.
Iran has been a World Cup qualifier out of Asia four times previously, all since 1978. Advancing past the group stage for the first time likely will require a victory over Portugal; a draw would do the trick only if Spain loses by multiple goals to Morocco.
"We are restless for the last match to come," Iran forward Karim Ansarifard said. "This is the time for redemption."
Iran lost to Spain , but only 1-0 in a match that featured numerous promising but unconverted scoring chances. So while Iran was disappointed with the result, it was pleased with its competitiveness.
"It was important to us to be proud when leaving the pitch and make the world respect our football," Queiroz said. "I think we did that, despite the result. We are more confident as a result and will be full of hope when we face Portugal."
They'll need more than hope to stop Ronaldo, who has scored four times - three in a draw with Spain - placing him among the leaders in goals for the tournament. He also is the world's active leader in international goals with 85 and showing little sign of slowing at the age of 33, leading Portugal coach Fernando Santos to compare his superstar forward to port wine.
Ronaldo also will be a fan favorite in Saransk, the smallest of Russia's 11 World Cup host cities , where his arrival is the talk of the town.
Queiroz was Portugal's coach from 2008-10, a stint that ended shortly after a second-round, 1-0 loss at the World Cup in South Africa to eventual champion Spain.
Reportedly, Queiroz did not get along with Ronaldo, the very player who will now be the focus of his defensive scheme.
Upon Portugal's elimination from the 2010 World Cup, Ronaldo was asked to explain his team's failure and responded by saying Queiroz should be the one to answer that question - a comment widely taken to mean that Ronaldo thought Queiroz was to blame.
When asked about having to coach against Ronaldo in a pivotal group finale, Queiroz said renowned film director Martin Scorsese couldn't write a better script.
How's that for a compelling subplot?
Ronaldo's presence alone should be enough to make Portugal confident about its chances of advancing. But teammate Jose Fonte sounds pleased with the level of play across the squad, even though no one other than Ronaldo has scored.
"We have four points. We are in first place in the group; only Spain is ahead with less yellow cards. We are satisfied with the quality we have," Fonte said. "We want to do better, but no alarms."
Added Santos: "We have to be aggressive, not to allow the opponent to play. We need to win more individual battles, more one-on-one duels, and to put our full offensive capacity on display."
A former goaltender, Queiroz has built Iran into arguably Asia's best defensive team.
Iran did not allow a goal in nine of 10 World Cup qualifiers. Iran has remained tough to score against in Russia, shutting out Morocco and allowing only one goal to a Spanish team which scored three times against Portugal.
Portugal midfielder Joao Moutinho fell ill recently with the flu. But for now, he is expected to be available to play against Iran.