Atletico drew 1-1 at the Camp Nou with Neymar scoring the equaliser for Barcelona, following Diego's stunning opener for the visitors, but while Simeone's men will have home-ground advantage next week in the second leg, the Argentine coach maintained the tie is evenly poised.
An away goal and a draw on the road generally set up two-legged ties for the team that play at home second but Simeone refused to get carried away with Atleti's chances after the first leg.
"I'm leaving happy with the effort and the result is good, although everything is in the air," the 43-year-old said.
Simeone took a risk in Barcelona, starting striker Diego Costa, despite the 25-year-old having failed to complete training on Monday, and the gamble backfired.
Costa limped off before the half-hour mark, which forced Simeone to push David Villa up front and bring on Diego to play in the hole.
While Diego scored Atleti's goal, rifling an incredible shot into the top corner from 25 yards, Simeone conceded the introduction of the Brazilian left his team without much pace up front and the coach indicated he might go with a different option in the future, if Costa's injury proves to be long-term.
"We lost speed in the front," Simeone said.
"We'll see what the tests say regarding the amount of time he's (Costa) out.
"We'll make use of Raul Garcia, Villa, Adrian Lopez."
Neither Raul Garcia nor Adrian Lopez were on the bench against Barcelona.
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