If football was determined by statistics, Fernando Hierro’s men would have won at a canter. By this game’s end Spain had enjoyed almost three times as many efforts on goal as Iran, not to mention 78% of possession.
Goals are the only currency worth holding in this sport and, mercifully for Hierro, Spain came out on top there too. Yet for all they were continually in the ascendancy, they found themselves separated from their far less illustrious opponents by a single deflected effort off the shin of Diego Costa.
That is not to Spain did not deserve their win. But the efforts of Carlos Queiroz’s Iran side should not go unnoticed: they made this a very tricky evening for many people’s favourite to win this year’s World Cup.
Here are five things we learned from a fascinating evening in Kazan.
1 The favourites continue to struggle to break teams down
This may well have comprised the most extreme example yet, but a common theme throughout the World Cup so far has been the struggle of more favoured sides to break down their supposedly lesser counterparts.
Spain must have felt they had been transported to 2010 or 2012, back when tiki-taka was in its zenith. The side that won the World Cup in South Africa eight years ago scored just eight goals in the process, a statistic that arose more from opposing sides being unwilling to come out from their shells rather than the Spanish overplaying - though that undoubtedly played a part too.
It is unlikely that anyone else Spain face this summer will sit quite so deep as Iran did for most of this game, but it remains that the strongest nations in the tournament continue to look somewhat nonplused in the face of stout defence.
In fairness to Hierro's side, it is they who have showed the most ingenuity in trying to breach the wall in front of them; at times, the interplay between David Silva, Isco and Andres Iniesta was mesmerising.
But their goal came via fortune rather than design. The minnows continue to show their worth in Russia.
2 Diego Costa does not fit, but he remains key
For the second game running, Diego Costa scored. Just as his powerful finish against Portugal was crucial in restoring parity, here his 'strike' was the difference between an expected victory and a galling draw.
Yet Costa continues to stand out like a sore thumb in this side. Take even a fleeting glance at this Spanish team and it is easy to identify who among their midst was not raised in the ways of the nation. Costa, born in Brazil, did not arrive in Spain until he was almost 20, and his bullish, physical approach appears in stark contrast to the more delicate style of those around him.
It is difficult not to wonder whether Spain will come unstuck against better opposition, such is the difference between them and their striker. They drew criticism against Italy at Euro 2012 for starting that game with no recognised forward, but on this evidence it is easy to see why; their style dictates that the man leading the line must drop deep, link play and encourage midfielders to rush on ahead of him.
Costa does none of that. What he does do is score goals and, especially now, that is all the more important. His winner was lucky, an attempted clearance that merely bounced off him, but it summed up his bulldozing approach. In a side that is masterful in possession, but too often does not convert it into goals, his is a quality Spain cannot do without.
Diego Costa might not be what this Spain team wants, but he is precisely what it needs right now.
3 Iran are no joke
Where Saudi Arabia and Egypt's influence on this World Cup has been almost non-existent, Iran have made their presence felt, and will have done so even if they fail to beat Portugal and progress into the round of 16.
Carlos Queiroz suffered just the 11th defeat of his seven-year stint as Iran manager on Wednesday evening, and it was easy to see why the former Portugal and Real Madrid manager has enjoyed such a successful time in charge of Team Melli.
Their approach was entirely negative from an attacking point of view, but when faced with the superstars in front of them it was also their only option. Costa's flukey finish was all the more disappointing to see given the waves off incisive passing they had previously managed to repel.
What spoke even louder about this side's potential was their response to that goal. It was tempting to wonder whether they had sat so deep because they didn't know how to do anything else, but their subsequent search for an equaliser disproved that notion.
Saeid Ezatolahi's thunderous finish caused pandemonium both in the stands and on the field, only to be rightly ruled out by VAR. Then, with just seven minutes remaining, Vahid Amiri made a mockery of Gerard Pique's standing as one of the best defenders in the world, nutmegging the Barcelona man before firing a cross straight onto the head of Mehdi Taremi. The latter should have scored, but the fact they created the chances at all was indicative of a side that plenty had underestimated before this summer.
4 Portugal's progress is in no way assured
After last Friday's thrilling 3-3 draw between Spain and Portugal, it was easy to assume that both sides would, as had been expected, progress to the next round.
That still seems the most likely outcome, but following this spirited display by Iran and Portugal's dour lunchtime battle Morocco, it would be rather presumptive to discount the chances of Queiroz's men entirely.
Portugal did, of course, win that game, saved once more by Cristiano Ronaldo. Looking distinctly average, but winning anyway has become their niche in recent times. Two years ago it won them the European Championships.
But as long as they fail to convince then they will remain in danger of coming a cropper. Their fortune, or Ronaldo's form, may just come to an end soon. Don't bet against it being next Monday evening in Saransk.
5 This Spain side is vulnerable
David de Gea's goal might have gone unbreached, but there can be little doubt that Fernando Hierro's men can be gotten at.
Perhaps it is down to the upheaval brought about by Julen Lopetegui's sacking just one week ago, perhaps it is a natural offshoot of the fact they spend most of the time attacking.
More than likely, it is a combination of the two, as well as the natural waning of an ageing backline.
Whatever the explanation, Spain again showed vulnerability in Kazan. As mentioned, Taremi really should have salvaged a point, heading the ball over the bar from inside the Spanish six-yard box.
When forced to defend, comfort looked far from their grasp. Against Portugal they shipped three, and while those came via the majesty of Ronaldo, it is impossible to look upon this side and not wonder if their defensive toils will be exacerbated come the later rounds.
Listen to the RealSport football writers discuss all the action from Day 7 of the World Cup in Kremlins in the Basement: RealSport’s daily World Cup podcast.
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