The stakes are set to rise on Friday in Groups A and B with England, Ecuador and the Netherlands able to progress to the last 16 at the World Cup with victories while hosts Qatar face the prospect of elimination should they lose to Senegal.
Wales and Iran launch the action on the sixth day of competition at the Ahmad Bin Ali Stadium. Wales, playing their first match at the World Cup since 1958, salvaged a 1-1 draw against the United States in Group B on Monday night after Iran had been dispatched 6-2 by England.
"Iran are a good team," said Wales skipper Gareth Bale.
"They're not at the World Cup for no reason. It will be a physical and mental challenge but we're ready for it. They need to win and we need to win so it should be an exciting game."
England will take top spot in Group B should they see off a United States side that will be smarting over its failure to capitalise more ruthlessly on its first half domination over Wales.
"We've been working over the past three and a half years on our style of play and how we want to execute it on the field," said US boss Gregg Berhalter.
"We think there are areas that we can exploit and where we can hurt England. We know they're a good team and that they have threats.
"We're going to have to be cautious about those threats but we want to play our game."
England, semi-finalists in 2018, have been buoyed by the news that skipper Harry Kane has recovered from an ankle injury and will lead the attack.
"We've got to perform," said England boss Gareth Southgate.
"We know they'll be highly motivated so we've got to be at our best.
"The risk for us is that we think because we played well against Iran we can go through the next game easily. We have to find that reset button and have the same determination."
Qatar go into their tmatch against Senegal hoping to avoid the ignominy of joining South Africa as the second host in the 92 year history of the competition to fail to advance out of the group stages.
Senegal, who come to the World Cup as African champions, are trying to reach the second round for the first time since their spectacular run to the last eight in 2002.
"We played well despite the defeat to the Netherlands who are one of the best teams in the world at the moment," said Senegal boss Aliou Cissé.
"We and Qatar have our backs against the wall so it will be an extremely important game.
"But I'd like to think our experience of being in such circumstances at other big tournaments will be able to help us."
Just after Qatar and Senegal finish their battle for survival, the Netherlands and Ecuador clash at the Khalifa International Stadium. Both won their opening games 2-0 against Senegal and Qatar respectively.
Victory for either team will guarantee progress to the last-16.
