Spain midfielder Iniesta was instrumental as Barca dominated their first-leg clash at Stamford Bridge only to lose to a Didier Drogba strike on the stroke of half-time.
Alexis Sanchez, Cesc Fabregas and, in the dying seconds, Sergio Busquets all missed gilt-edge chances for the Catalan side while Sanchez and Pedro also struck the woodwork.
It means Chelsea will carry a slim advantage into the return at the Nou Camp on Tuesday with the winners advancing into the final to meet either Real Madrid or Bayern Munich.
"The result is unjust but we knew that Chelsea are a team that take advantage of their opportunities," Iniesta told the club's official website.
"We were off target in front of goal but we still have the return leg at home.
"We have the feeling that we created a lot of clear chances, the only thing we were lacking was the final touch. Sometimes this happens.
"We'll try to be more effective in the return leg, we have confidence in our ability to overturn today's scoreline.
"We have had an adverse result and we have to work harder seeing that we're capable of doing it. It's not an issue of luck."
Next up for Barca is the season's second el clasico in the Primera Liga. Pep Guardiola's men go into the game four points behind leaders Real.