It took an exceptionally fortunate goal from Diego Costa to defeat Queiroz's side, who frustrated their opponents for more than 50 minutes - as well as squandering several opportunities to score in the second half.
Speaking after the match, and quoted by Reuters, Queiroz said: "We go for it, with great belief and great determination to try to win the game. When we arrived, no-one gave us a chance, but we still fight for our dreams."
Quoted by the BBC, the Portuguese - who has managed Iran since 2011 - also expressed his disappointment with the result against Spain, insisting that it wasn't a fair reflection of his side's performance. "There's no doubt Spain play wonderful, stylish football but we deserved more for the way we played," claimed Queiroz.
Despite their defeat against La Roja, Iran's fate is still in their own hands. Whatever happens in Spain's final group match against Morocco, the Iranians know that a win over Portugal will see them into the round of 16.
While few would expect Iran to defeat Cristiano Ronaldo's side, it would be unwise to write them off - they didn't make life at all easy for Spain, while Portugal looked eminently beatable in their unconvincing 1-0 win over Morocco.
Queiroz sounded upbeat about his side's prospects against the reigning European Champions, as he likened his team's situation to a tennis match: "If you think of it like tennis, we had one match point today and we will have another against Portugal. Everything is still open. We are still alive and still dreaming."
Queiroz is now at his third World Cup, having managed Portugal in 2010 and Iran in 2014. He also led South Africa to qualification for the 2002 World Cup, but resigned before the start of the tournament.