David Villa spurned an early chance in the first leg at Camp Nou and Andres Iniesta's shot at the other end was blocked by Diego Godin before Villa drew a good save from Jose Pinto in first-half stoppage time.
Brazilian forward Diego, who had come on to replace Atletico's injured talisman Diego Costa after half an hour, unleashed an unstoppable drive to put the visitors ahead on 57 minutes.
But compatriot Neymar drew Barcelona level 14 minutes later after a fine pass from Iniesta.
The visitors were clinging on by the end, relying on goalkeeper Thibaut Courtois to make outstanding saves, denying first Iniesta and then Lionel Messi.
Diego Simeone's side's desperation was underlined by the fact six of their players picked up yellow cards, while just two Barca players received cautions.
But the visitors' resolute defending paid off and meant a fourth successive draw in the meetings between the two teams this season to leave both with all to play for in next week's second leg at the Vicente Calderon.
Costa was named in the starting line-up despite retiring prematurely from his side's training session the previous evening, but succumbed to a hamstring injury which is almost certain to rule him out of the return leg in Madrid.
Villa came in for the suspended Raul Garcia and had the first attempt of the night, trying his luck from 30 yards but firing well wide.
The former Barca striker had a clearer opportunity just moments later, receiving the ball after Arda Turan had intercepted Pinto's poor kick, but shot wide of the far post.
Barca had to make their first substitution of the night after just 12 minutes, Gerard Pique struggling after an aerial challenge and forced to come off for 23-year-old Marc Bartra, who shone in a rare moment in the spotlight.
Despite the early openings, the game soon took the same shape of the three cagey encounters between the two sides this season, with Barca taking until 23 minutes to test Courtois, Neymar heading softly into the Belgian's hands.
Their next attempt was by the majestic Iniesta, played in after Messi had danced around Miranda, but Godin threw out a leg to block the shot before it could get to Courtois. Then Davi Alves crossed to Messi, but the Argentinian could not get enough power on his header, and ended the night failing to get on the score-sheet for the first time in six games.
Neymar had a final go for Barca before half-time, his ambitious long-ranger flying just a little high of the crossbar, while Villa tested Pinto at the other end.
The second half began like the first with little space opening up, so it required a goal out of nothing to break the deadlock. That is what Diego produced when he picked the ball up on the right hand side following a free-kick, beat Xavi then drove the ball from an improbable angle and range into the top corner.
At the other end, Sergio Busquets saw his effort pushed away by Courtois. Messi then tried to head a cross from Alves towards goal but it hit his chest on its way over the bar.
But Barca got their equaliser with 19 minutes remaining when Iniesta split the visitors' defence with an exquisite pass to Neymar inside the area, the Brazilian shooting into the far corner of Courtois' net with one touch.
The goal galvanised the Camp Nou side and rattled the visitors. Just a few minutes later Iniesta went looking for goal, only denied by an inspired leap by Courtois, who finger-tipped the ball out for a corner.
Barca had a near monopoly on possession after the equaliser, but Courtois made one final save of the night to keep out Messi's late free-kick.
Atletico will feel relieved to return to Madrid with the tie evenly balanced, having scored a crucial away goal to boot.