Luis Suarez scored twice as Barcelona fought back to beat 10-man Atletico Madrid in an action-packed Champions League quarter-final first leg.
Atletico scored a potentially valuable away goal when Fernando Torres blasted in a clinical first-time shot.
But the game turned when Torres was sent off before half-time for two needless bookings inside seven minutes.
Holders Barca upped the tempo after the break, Suarez prodding in the equaliser then powerfully heading in the winner.
However, the Uruguayan had been fortunate not to be shown a first-half red card for kicking out at Atletico right-back Juanfran.
The teams will meet again in the second leg at the Vicente Calderon next Wednesday.
Relive all the drama from Camp Nou
Torres goes from hero to zero
Torres, 32, has failed to rediscover anything like prolific form since returning to boyhood club Atletico - but his goal here was arguably the most important of his second spell.
The former Liverpool and Chelsea striker showed the clinical edge which characterised the early part of his career as he latched on to Koke's defence-splitting pass to fire in through Barca keeper Marc-Andre ter Stegen's legs.
However, his side's tactical masterplan - grab the away goal and sit tight - was blown apart by his dismissal.
Torres was shown his first yellow card for clipping Barca forward Neymar, then saw red moments later when he needlessly clattered into the back of midfielder Sergio Busquets close to the halfway line.
Atletico manager Diego Simeone was incensed by the decision of German referee Felix Brych, who upset Los Rojiblancos by sending off Arda Turan in their Champions League quarter-final defeat by Real Madrid last season.
And the Argentine may well believe his team were the victim of a further injustice when the official seemingly missed Suarez lashing out at Juanfran near the dead-ball line.
"I can't say what I think, but I am not angry with Fernando for sure," said Simeone.
Atletico's tactics (almost) pay off
Eleven men behind the ball when not in possession, staying compact and narrow to limit the home side's space - Barca knew exactly the tactics Atletico would employ.
But the Catalan team were powerless to stop Atletico's stubborn effectiveness in the opening hour.
Atletico wanted to frustrate Barca, refusing to allow the home side to play their free-flowing football in a relatively comfortable first half capped by Torres' opener.
After the break, the hosts showed more urgency - and the intense pressure finally told.
Neymar curled the ball against the bar and missed another gilt-edged header, while Filipe Luis's superb last-ditch challenge stopped Lionel Messi pouncing to convert a loose ball.
But eventually the pressure told.
Suarez, who had been kept relatively quiet by Uruguay team-mate Diego Godin, instinctively diverted in Jordi Alba's mis-hit shot, then generated remarkable power to head in Dani Alves' pinpoint cross.
Barca continue Atleti dominance after El Clasico defeat
Barcelona came into the match on the back of Saturday's 2-1 home defeat by arch-rivals Real Madrid, a loss that ended the Catalan side's 39-match unbeaten run.
And Atletico appeared to take plenty of encouragement from their neighbours' win at Camp Nou.
However, the numerical advantage after Torres' dismissal allowed Barca to secure their seventh successive win against Simeone's team.
The Spanish champions have beaten Atletico in both La Liga matches this season, helping them move six points clear of their opponents.
Now Barca appear to be the slight favourites to reach the semi-finals as they attempt to become the first club to win back-to-back Champions League titles.
Man of the match - Dani Alves (Barcelona)
Barcelona manager Luis Enrique: "We must appreciate the difficulty in playing against Atletico. With this attitude and these players we will go to the end of the world."
Atletico Madrid manager Diego Simeone: "Beyond the inequality there was in the match, we leave with a situation that allows us to have hope.
"I am very happy with my team. Once again, we started winning, we were doing very well."
Atletico Madrid left-back Filipe Luis told BT Sport: "It is an awful result. It could be a lot worse but also a lot better.
"We shouldn't have got the red card, it was totally unfair. It is not easy to play against Barcelona in the Champions League. We know it is really dangerous if they go out in the quarter-finals. We have to play against everyone and everything.
"We know it will be really difficult to go through but I think we are still alive. It is possible."
Stats of the day
Fernando Torres has joined Zlatan Ibrahimovic and Andriy Shevchenko in scoring against Barcelona in the Champions League for two different clubs
Barcelona have only kept one clean sheet in 13 Champions League/European Cup games against Spanish opposition, that was against Real Madrid at the Bernabeu in April 2011
Lionel Messi, Luis Suarez and Neymar have scored 44 of Barcelona's 53 Champions League goals since last season (83%)
Barcelona are one of two clubs still unbeaten in the Champions League this season, the other being Real Madrid. They have won 18 of their 22 games in the competition since last season, losing two and scoring in all 22 games
No player has more assists at than Dani Alves in the past two Champions League campaigns (7 - joint with Cristiano Ronaldo)
Luis Enrique has won all 11 of his Champions League games at the Camp Nou as Barcelona manager
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