Diego's wonder-strike for Atletico was cancelled out by Neymar's effort at Camp Nou, leaving the tie finely balanced heading into the return leg at the Vicente Calderon next week.
Barca's last visit to Atletico, in La Liga back in January, ended 0-0 - a scoreline that would be enough to see Diego Simeone's side through on away goals.
"It's wide open," said Barca playmaker Xavi. "We have to try to score goals there and that will lead us to victory.
"Atletico are an intense team and it was very difficult for us to find space. We will have to be very patient."
Barca goalkeeper Jose Pinto, meanwhile, conceded Atletico have the upper hand in the tie.
"Atletico have the advantage but we will not give up until the final minute," he said.
"I approach each match like I always have, I maintain my excitement and I work hard.
"I've always been ready for my chance and I want to continue to enjoy each day."
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