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.
A final score favourable 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 tomorrow'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."
Portugal, the defending European champions, are tied with Spain at the top of Group B with four points each. Iran are right behind with three, thanks to their opening 1-0 victory over Morocco.
Iran have 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 lose 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 were disappointed with the result, they were pleased with their competitiveness.
- AP