The goal was fortuitous, with an Iranian defensive clearance hitting Costa and the ball rebounded past the goalkeeper. The 29-year-old has now scored three goals at the tournament, and is on the same place among leading scores of the tournament with Russia's forward Denis Cheryshev.
Portugal’s Cristiano Ronaldo is currently on course to win the Golden Boot for the World Cup’s top scorer, having netted four times in the space of two games.
"I have scored three goals, but winning is more important than scoring. The match [against Iran] was difficult. I hope that I and Cristiano [Ronaldo] will continue scoring," Costa told journalists.
Meanwhile, Spain head coach Fernando Hierro said Wednesday night that the half time break helped his team psychologically during their har-fought play with Iran.
“We need to be patient and play calm in the match with Iran in order to score. The break helped us, we made corrections, took a look at ourselves and encouraged the boys. It was important to play a more expansive game, to move around more. The break was important psychologically. It was important to believe in ourselves, no matter how difficult the match was. Now we have four points and we can be content with ourselves,” Hierro told journalists.
Moreover, Fernando Hierro said that the match against Iran turned out to be unexpectedly difficult for his squad.
Hierro added that this summer's World Cup wouldn't be easy for Spain.
"We will draw conclusions and continue playing as a team. It will be a very difficult tournament. There will be no easy matches, but we believe in the way we've chosen and will develop," he said.
Spain head coach also paid tribute to Costa, who has scored three times at the World Cup so far.
“[Costa] is a man who does not compromise, he is a fantastic player and can do even more. Diego Costa puts himself about, he works well with the ball,” Hierro said.
“I am satisfied with our position in the group. We have four points, our chances are not bad. It was a difficult match, but the main thing is we won. I like this Spanish team and I feel great,” Isco told reporters after the game.
Spain and Portugal are currently at the top level of Group B with four points, while Iran are a point further back on three. Spain will face Morocco in their final group game on June 25 in Kaliningrad.
The 2018 FIFA World Cup Finals kicked off on June 14 and will continue until July 15, with the matches being played in 11 cities across Russia.