The Reds held a 1-0 advantage ahead of the return match at Anfield, but that was cancelled out when goalkeeper Jose Reina let a David Templeton shot squeeze through after 85 minutes.
Extra-time appeared to be on the cards but Luis Suarez then grabbed an equaliser two minutes from the end to see Liverpool sneak into the group stage 2-1 on aggregate.
"We knew it was going to be tough," he said on ESPN. "We made more hard work of it than we should have done.
"We were a little bit wasteful in front of goal.
"However, the manager stressed to the team 'don't go down under pressure', and I think we bounced back well.
"We created lots of chances we didn't finish though and we have to be more clinical in front of goal. That was a lesson for us."