Both sides go into their third Group B game hoping that it will not be their last appearance at Russia 2018, fifa.com reported.
The difference is that a draw would be enough for Portugal to progress, while Iran needs a win to secure qualification and break new ground in the process.
The Iranians showed themselves to be formidable opponents in their first two matches, particularly impressing in defense. Their resilience was rewarded with a clean sheet against Morocco, while one mistake cost them against Spain.
On the other hand, they were far more threatening going forward against La Roja, creating a number of clear-cut chances. Had they had a bit more luck, they could have scored more than the solitary goal they managed against Morocco.
It is no secret that this Portugal side revolves around Cristiano Ronaldo, to whom Portuguese are indebted for their four points to date.
Having bagged a hat-trick to earn the European champion a share of the spoils against Spain, he hit the winner against Morocco to take his country a step closer to qualification.
However, with A Selecção das Quinas determined to avoid a repeat of their group-stage exit at Brazil 2014, Ronaldo's teammates know that they cannot afford to put all their eggs in the basket of their talismanic captain, lest he have an off day in front of goal.
The two teams have faced each other at the World Cup once before. That was in the Germany 2006 group stage, with Portugal running out a 2-0 winner and a certain youngster by the name of Cristiano Ronaldo getting the second goal.
The forward has well and truly come of age since then and is now the team's captain.
He is the only current squad member on either side to have featured in that game. Iran's Masoud Shojaei was also at the tournament, but did not play that day.