Barca won the first leg of the quarter-final 1-0 at Camp Nou, as Lionel Messi tapped in the rebound from a saved penalty with just five minutes to play.
Atletico defended in numbers for much of the contest and the late goal was a cruel blow to the Spanish champions.
Simeone told Atletico's official website: "I see the second leg with open possibilities.
"[It is] against a rival that plays well. Due to the result, it's an open qualifying round.
"I thought the game was controlled defensively [by us], with few outlets for counter-attacks.
"The goal came and now we'll have to wait for the second leg."
Atletico defender Miranda is looking forward to the vocal support his side will get in next week's second leg at Vicente Calderon.
"It's a shame because we played very well," Miranda told Canal+.
"It [qualification] is achievable. With the support of our fans, we can comeback from this result.
"Our fans support us whenever we need it and now, it surely isn't going to be any different. We look to comeback at the Calderon."
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