Iniesta, who celebrated the birth of his baby at the weekend by opening the scoring inside two minutes against Shakhtar, also refused to assume a semi-final place was now theirs.
He said on his club's website: "We would be wrong if we thought that it was already done.
"I think everybody has seen the opportunities Shakhtar had. They created a lot of chances, they've hit the post, they had a one-on-one. In the return match we have to be careful."