Hierro: Spain must improve on the job

A second-half strike from Diego Costa secured all three points for Spain in Kazan on Wednesday, where the deafening sound of vuvuzelas and singing from a predominantly Iranian crowd added to the challenge.

After an intense encounter in which Iran frustrated Hierro's team of superstars for long periods, Costa admitted he got "lucky" when his strike rebounded off defender Ramin Rezaeian and into the Iranian net.

Spain, who drew 3-3 with Portugal in their opening World Cup match, held on for their first win to move level with the Portuguese on four points in Group B after the European champions earlier beat Morocco, courtesy of another Cristiano Ronaldo goal.

Hierro said he has reason to worry after a string of surprising opening-round results in Russia.

Defending champions Germany were upset by Mexico, Brazil were held by Switzerland, Iceland drew with Argentina and France were lucky to escape with a 2-1 win over Australia.

"This is the World Cup, and not one single game is going to be easy," Hierro said. "We can improve, and I hope we will keep winning while we do so, but nobody is giving anything away easily."

Hierro said danger loomed next Monday against Morocco in Kaliningrad, with Iran, on three points, still in the mix.

"We are in a very even group, where everything is equal, as they are in the other groups," he added.

"In certain groups teams have already qualified (for the last 16) but our group is very tough. We have no option but to secure all three points against Morocco."

Spain's bid for a second World Cup title eight years after their first, began in the worst-possible fashion, with coach Julen Lopetegui sacked on the eve of the tournament after Real Madrid announced he would be joining the club in July.

Hierro, who scored 29 goals in an 89-cap career with Spain, was promoted from his role as sporting director in time for their opener with Portugal.

Carlos Queiroz's Iran also endured difficulties in the run-up to the World Cup.

Both Greece and Kosovo cancelled scheduled friendlies and sportswear giant Nike refused to supply the players' boots due to US sanctions.

Queiroz, however, insisted their "dream" of securing a historic first qualification to the second round remains intact.

"Coming into this tournament, people gave us no chance but we still have chances to qualify for the second round. We'll fight for our dreams," he said.

"We lost top spot in the group but the reality is this: our dream is not over. Against Portugal, it will be match point for us."