Spain look to ease pressure on them with their first win of FIFA World Cup 2018, while Iran aim to register their second consecutive triumph in the Group B match at Kazan Arena on Wednesday.
Spain tied 3-3 with Portugal on Friday in their first international match under the newly-appointed head coach Hierro, who took the job just two days before the mega tournament started as his predecessor, Julen Lopetegui was sacked for announcing his appointment as the Real Madrid coach for the next season.
Spanish playmaker Isco believes that Wednesday's match against Iran will determine their World Cup destiny as they seek to register their first win in Russia.
Nevertheless, Spain players are rallying behind goalkeeper David De Gea as they prepare for their second group game at the World Cup against Iran in Kazan on Wednesday.
Moreover, Portugal play their second match against Morocco earlier on Wednesday and a win for Portugal will mount tremendous pressure on Sergio Ramos & Co.
On the other hand, Iran kicked off their campaign with a hard-fought 1-0 win against Morocco, thanks to a late own goal by Aziz Bouhaddouz. Iran now sits at the top of the pile as they are the only Group B team with a win so far, an achievement that sparked incredible celebrations in the streets of Tehran and elsewhere throughout the Islamic republic.
Coach Carlos Queiroz conceded that Iran now face one of the biggest challenges in their World Cup history, but maintained that they can "make the impossible possible".
"If the game against Morocco was the World Cup final for us, the game against Spain will be the Universe Cup final," said the Iran coach who also has the experience of coaching Real Madrid, the royal club of Spain.
Iran have never beaten a European side at a World Cup -- their only previous victory was a 2-1 win over the United States in France in 1998.
Goalkeepers: David De Gea (Manchester United), Pepe Reina (Napoli), Kepa (Athletic Bilbao)
Defenders: Dani Carvajal(Real Madrid), Sergio Ramos(Real Madrid), Nacho (Real Madrid), Jordi Alba(Barcelona), Gerard Pique (Barcelona), Nacho Monreal (Arsenal), Cesar Azpilicueta (Chelsea), Odriozola (Real Sociedad)
Midfield: Sergio Busquets(Barcelona), Andres Iniesta (Barcelona) Saúl, Koke (both Atletico), Thiago (Bayern) David Silva (Manchester City), Isco, Marco Asensio, Lucas Vázquez (all Real Madrid)
Forward: Iago Aspas (Celta), Rodrigo (Valencia), Diego Costa (Atletico)
Goalkeepers: Amir Abedzadeh, Alireza Beiranvand, Mohammad Rashid Mazaheri
Defenders: Rouzbeh Cheshmi, Majid Hosseini, Mohammad Khanzadeh, Milad Mohammadi, Pejman Montazeri, Morteza Pouraliganji, Ramin Rezaeian
Midfielders: Vahid Amiri, Ashkan Dejagah, Omid Ebrahimi, Saeid Ezatolahi, Ali Gholizadeh, Ehsan Hajsafi, Masoud Shojaei, Mehdi Torabi
Forwards: Karim Ansarifard, Saman Ghoddos, Reza Ghoochannejhad, Alireza Jahanbakhsh, Mehdi Taromi