Champions in 2010 and among the favourites this year, Spain's World Cup ambitions were kept in check, almost single-handedly, by a stunning Cristiano Ronaldo hat-trick.
The draw came just two days after Spain's campaign was thrown into disarray by the shock sacking of coach Julen Lopetegui following an untimely announcement by Real Madrid that he would join the 13-times European champions after the tournament.
Fernando Hierro, Spain's sporting director, is now at the helm but barely a week into the tournament La Roja -- expected to join Brazil, Germany and France in the latter stages -- have endured more drama than they would have wanted or expected.
"It's a crucial match that will determine our World Cup destiny," said Isco. "We want to score from the opening minute, even though that won't be easy.
"We will stick to the style that defines us as a team, but we have to pass the ball around a lot more and maintain possession. If we play quickly across the pitch, the chances will come. I hope we score quickly."
Iran kicked off their campaign with a 1-0 win against Morocco, thanks to a late own goal by Aziz Bouhaddouz, piling the pressure on Spain at Kazan Arena on Wednesday.
Iran sit top of the pile as the only Group B team with a win so far, an achievement that sparked incredible celebrations in the streets of Tehran and elsewhere throughout the Islamic republic.
Coach Carlos Queiroz concedes Iran now face one of the biggest challenges in their World Cup history, but maintains they can "make the impossible possible".
'Universe Cup final'
"If the game against Morocco was the World Cup final for us, the game against Spain will be the Universe Cup final," said the former Real Madrid coach.
"It was not a miracle that we won. What can happen once in a while is a group of people, when they are united, can create super stories and super things.
"Our attitude is to try and make the impossible possible."
Yet keeping the Spanish armada at bay to claim the point that would boost hopes of qualifying for the last 16 looks a tall order.
Iran have never beaten a European side at a World Cup -- their only previous victory was a 2-1 win over the United States in France in 1998.
Despite the frustration of conceding an 88th-minute equaliser to Ronaldo following two goals from Diego Costa and a stunning strike from Nacho, Isco believes Spain's resolve remains intact.
"We had a setback but we stuck together and got on with the job," he said.
"We saw that in the first match. We never gave up, even after conceding a goal in the fourth minute. That shows what this team is all about. We'll never stop fighting."
By AFP's Justin Davis