La Roja will face Iran in Kazan’s Kazan Arena on Wednesday in Group B of the 2018 World Cup.
"Wednesday's game is like a final," said Iniesta. "If we win it will give us an advantage in our group and then we can start to look towards the later stages.
"It will be a tough game but you have to remember we're a really united team that's been together for many years,” the Barcelona captain added.
"We trust each other blindly."