The Spanish champions won the encounter in Manchester 2-0, controlling the middle of the pitch for long periods while City's expensively-assembled team rarely threatened.
"They are a strong team with good players but they knew they were up against Barca and that we can cause them a lot of problems," Iniesta told Reuters.
"They had to choose the right balance between attack and defence. It is a tactical war."
The midfielder believes that City will have to be more adventurous in the return leg on March 12, which could also work in Barca's favour.
"They will have to attack more and we will try to take advantage of this by making the most of the spaces that they leave open," he said.
City striker Sergio Aguero has recently returned from injury to boost their attack and Iniesta knows he is a danger.
"El Kun (Aguero) plays at a very high level and he is an important player for them, but we will try to give them as few opportunities as possible to cause us problems.
"It is a difficult tie for us and while we have had one good result so far, we will have to be prepared and do things well again in order to get through to the next round."
World Cup holders Spain continued their preparation for this year's tournament with a 1-0 victory over Italy on Wednesday and Iniesta believes they are on track to repeat their 2010 success.
"Against Italy the sensations were good and I am looking forward to the World Cup," he said.
"We will want to get off to a good start and then go step-by-step. It won't be easy but we have to have confidence."
The current Spain side have already had a taste of playing a tournament in Brazil, after last year's Confederations Cup, where they reached the final before losing to the hosts.
"I think it was a good display from us at last year's Confederations Cup as we reached the final," Iniesta added.
"In the final we didn't play well but our aim was to get to the final and we were up against a very strong Brazil side."
Iniesta feels that Atletico Madrid's Diego Costa, who was born in Brazil but has decided to play for Spain, will give them an extra threat in attack.
"He can offer us a lot. He is the kind of player that we are not used to having and his performances this year (for Atletico) have been superb," he said.
- Sports & Recreation
- Sergio Aguero