Hierro: Nobody is winning easily in the World Cup, Spain have had it hard as we thought FIFA World Cup 2018 - Iran vs Spain Sit top of Group B ahead of final match

Diego Costa's rather fortuitous goal was enough to take Spain to a 1-0 victory over a resilient Iran, leaving Fernando Hierro to make clear that La Roja have had it as hard as previously thought.

La Roja are on course to progress into the knockout stage, with the team currently placed at the top of the group.

"Nobody is winning easily at the World Cup, we've had it as hard as we thought," he explained in a post-match interview with Telecinco.

"It's difficult to get into a rhythm with so much interruption. At half time we corrected some things and improved after the goal."

Few expected Group B to be as competitive as it has proven to be with Carlos Queiroz's Iran having pushed La Roja for much of the match on Wednesday evening.

Any two from Iran, Spain and Portugal can still progress to the last-16, something which Hierro believes indicates the strength of the tournament.

"Equality is at its maximum in this World Cup," he intimated. "Iran are a great team, with clear ideas.

"Queiroz has been working with them for seven years and they won't make things easy for anyone."