The two clubs came into the tie while in the thick of a hotly-contested title fight, and there was little chance of respite here as Atletico stunned their hosts to open the scoring inside 50 seconds.
Antoine Griezmann’s cross into the box was nodded to the back post by Clement Lenglet, where Julian Alvarez was waiting to prod the ball home.
The Argentine striker turned provider mere minutes later when he won the ball inside the Barca half and broke forward before playing a sublime through ball for Griezman to run onto, and the former Blaugrana forward showed excellent composure to fire past Wojciech Szczesny.
Hansi Flick’s men were visibly stunned and frustrated after conceding twice in six minutes, but their response was one that would have pleased the German coach.
In the 19th minute, Pedri slotted the ball into the bottom right corner after latching onto Jules Kounde’s cutback before the home side levelled the scoreline less than 120 seconds later when Pau Cubarsi popped up at the far post to nod home from Raphina’s corner.
Barca rounded off a brilliant first half of football by replicating their second goal minutes before the break, with Raphinha’s corner headed first time in at the far post by Inigo Martinez.
Atleti came out firing following the restart and almost equalised within minutes of the second half as Rodrigo De Paul picked out Griezmann with a defence-splitting pass, but the Frenchman’s effort was saved by Szczesny.
Lamine Yamal, having an unusually quiet evening, thought he had earned a penalty just before the hour mark after being brought down in the box, yet his appeals were waved away.
Los Colchoneros were threatening on the break against a high Barca defensive line, and the visitors thought they had equalised midway through the second period.
Angel Correa split the backline and sent Marcos Llorente in on goal and he laid the ball to Alexander Sorloth to fire in, but it was chalked off for offside. Cruelly for Diego Simeone’s men, Flick’s side went up the other end and notched a fourth goal.
Yamal brilliantly dribbled through the Atleti defence and laid the ball on for substitute Robert Lewandowski to tap into an empty net.
The contest wasn’t finished there however, as Atleti set up a mouthwatering second leg when Llorente drilled his finish into the far corner.
The scoring wasn’t finished there as Sorloth stunned the Barcelona faithful with a stoppage-time equaliser.
While the return match is in April, the sides will face off again before that in LaLiga, which will no doubt be another fascinating contest.