The 2010 champions head into the second match at Kazan Arena eager for a win under new coach Fernando Hierro, having been held to a 3-3 draw by Iberian rivals Portugal.
Hierro replaced Lopetegui after he was sensationally fired two days before the opener, but the 50-year-old's appointment triggered reports in the Spanish media that alleged players were divided over the change.
“We want to forget that change, it’s true that it wasn’t a nice thing for anybody and it was a difficult thing for everyone," Iniesta, seated alongside Hierro, told reporters at Kazan Arena on the eve of the Group B match.
"Right now we want to concentrate on what we’re doing and what we have.
"Have we any doubts about the coaching team? No, we don’t, we have never had any doubts."
Spain, with its mix of proven World Cup winners and young stars, will be heavy favourites to emerge from Kazan with maximum points, though the Carlos Queiroz-coached Iranians top Group B after beating Morocco 1-0 in their opener.
The opposing managers formed a mutual appreciation society on Tuesday, with Queiroz praising Hierro for uniting the side at short order, and the Spaniard describing the 65-year-old Portuguese as a "wonderful man".
"The Iranian team is a very strong team both defending and attacking, they have very strong opinions ... They are difficult to score against," said Hierro.
"It’s going to be tough, we saw how they played against Morocco.
"(But) we have analysed them and we know what they like to do, defending and attacking.
"Our opponents are very strong but on the other hand we do many things right so we have to trust in ourselves."
Hierro confirmed Dani Carvajal was fit and available to provide another option at right back but the coach may be reluctant to tip Nacho Fernandez out of the starting side given his brilliant goal against Portugal, which made up for giving away an early penalty.
Hierro was also resolute that goalkeeper David De Gea's place was assured despite the Manchester United stopper's tough night in the opener, when he let through one of Cristiano Ronaldo's three goals with a surprising blunder.
"De Gea is going to play tomorrow, we trust him 100 percent," said Hierro.
(Editing by Pritha Sarkar)
