A thrilling second half to the Clasico showdown in Catalonia saw Lionel Messi cancel out an earlier Gerard Pique own goal from the penalty spot, with the decision controversially given after Luis Suarez appeared to dive.
That was just the start of the drama, though, as Cristiano Ronaldo came off the bench to regain his side's advantage, before being dismissed for two cautions in quick succession - the latter for placing his hands on the referee when a penalty call went against him.
The 10 men of Real would go on to add a third late on thanks to Marco Asensio, meaning that they are in full control ahead of Wednesday's return leg at the Bernabeu.
Matteo Kovacic, filling in for the suspended Luka Modric, saw a cheeky attempt from range easily dealt with by Marc-Andre ter Stegen a minute into the match after the keeper's attempted pass was cut out.
There was a chance for Suarez up the other end soon after, taking down a ball over the top with his first touch and testing Keylor Navas from a slight angle with his second.
Isco picked out the side-netting and Casemiro's belter was hit straight at Ter Stegen in a first half lacking any real attacking quality, with Gareth Bale's snapshot late in the opening 45 minutes - helped over the bar by the Barca keeper - as close as either side came to an opener.
The contest certainly had an edge to it, though, as five players were shown a yellow card in the first half in a match that threatened to boil over at times without actually doing so in front of the 89,514 spectators.
Madrid made the breakthrough early in the second half through a Pique own goal, coming after Marcelo sent a dangerous cross into the box from the left which the centre-back horribly diverted into his own net.
That goal helped to liven things up as Barca created their best chance moments later, with Aleix Vidal's cross somehow making its way all the way through to Gerard Deulofeu, who was caught in two minds when well positioned and failed to pick out a teammate or the target with his shot-cross.
With the Catalans pushing high up the pitch there were plenty of gaps for the visitors to exploit, which Karim Benzema made the most of to get in behind down the left and pick out Dani Carvajal, only for the full-back's shot to be cleared off the line by opposite number Jordi Alba.
Suarez was the next player to come close, testing Navas with a smart header from eight yards out, while Ronaldo - introduced with an hour of the match played - did not take long to make an impact.
After sending one bicycle-kick attempt wide the Portuguese did find a way past Ter Stegen, yet the offside flag was correctly raised before he could celebrate.
Then came five minutes of drama as, after producing two big stops to keep out Messi, Navas was accused of tripping Luis Suarez inside the box - replays suggesting that the Uruguayan conned the referee into awarding the pen.
Messi sent Navas the wrong way to level things up at Camp Nou, only for Ronaldo to expertly cut inside and pick his spot from the edge of the box to put the La Liga champions back in front.
Then came the controversial red for Ronaldo, awarded after two yellows in quick succession - one for taking off his top to celebrate, the other for going to ground too easily under contract from Samuel Umtiti, which he did not respond well to.
Not that it mattered, as another second-half substitute in Asensio gave a further glimpse of his attacking capabilities by drilling the ball past Ter Stegen late on when played in on the counter to open up a two-goal advantage for his side.