Hierro will go up against Carlos Queiroz when Spain meet Iran and the pair have great mutual respect for each other, though the former Real Madrid defender downplayed the importance of their personal duel. The kickoff of the second half, however, saw the Spanish side pick of momentum in their chase for a goal, creating a couple of chances.
In the 54th minute, Ramin Rezaeian's terrible clearance richocheted off Costa's shin which left goalkeeper Alireza Beiranvand with no chance as Spain went ahead.
Saeid Ezatolahi, his team-mates and nearly the entire Iranian bench celebrated wildly before the referee ruled the goal out.
Iran did not concede a single goal until the last of their 10 final round Asian qualifiers when their spot in Russian Federation was already secure, at the same time creating enough going forward to win six of those matches. With Spain and Portugal both having secured a win and a draw and Portugal expected to trounce Iran on Monday, both Iberian countries will nearly certainly proceed to the knockout stage of the tournament, leaving Morocco and Iran out of the running.
Spain were hanging on, but time was running out for Iran to find a goal and snatch a point from this Group B encounter. Do not cut, copy or lift any content from this website without our consent.
Spain's new coach Fernando Hierro said after the match that he was happy for getting three points, noting that Iran are a strong team.
If anyone was going to breach the solid defensive wall so carefully constructed by the Iranians, it had to be the in-form Costa, even if his goal had more than a touch of good fortune about it, as an attempted clearance bounced from his knee and into the back of the net.
The goal took Costa's tally to three goals in the tournament and second in the scorers chart behind Cristiano Ronaldo, who has four goals.
"When I speak about my team, I speak about the 23 players", Hierro said.
With the unlucky 1-0 loss to Spain, Iran are now winless against European opposition at the World Cup.
After Wednesday, Team Melli will finish their group stage campaign on June 25 against Portugal, which will pose a different but equally hard obstacle.
David Silva sent a free kick straight into the arms of keeper Ali Beiranvand in the 25th minute for Spain's first shot on goal. "I hope things carry on this way, as long as the team does well out of it".
Iran continued to have the better of the efforts as the half wore on, with Mehdi Taremi missing two glorious chances.
Spain will face Morocco and Iran will take on Portugal to wrap up Group B play on Monday.
Queiroz did not reveal who the staff member was, but the Portuguese insisted his side were not giving up their World Cup dreams just yet.
Ramos also answered criticism by Queiroz, who brought up Ramos' clash with Egypt forward Mohammed Salah in the Champions League final after being told that Spain right back Dani Carvajal complained of Iran's tactics.