Vinicius Junior opened the scoring just before the break as Carlo Ancelotti's side mounted a spectacular comeback from their one-goal semi-final first leg deficit, with Benzema adding a second-half treble.

After netting three at the weekend against Real Valladolid in La Liga, Benzema repeated the trick to humiliate Barcelona on a painful night for coach Xavi Hernandez in front of almost 95,000 distraught fans.

Los Blancos trail their arch-rivals by 12 points in La Liga and were beaten by Barca in the Spanish Super Cup final in January, but triumphed here to reach the Copa final for the first time since 2014, where they will face Osasuna.

Madrid turfed out the record 31-time cup winners with a muscular performance on a spiky night in Barcelona, where they also ended a demoralising run of three consecutive Clasico defeats.

Ancelotti's team dominated in the first leg but fell to a 1-0 defeat after Eder Militao's own goal, and suffered a last-gasp sucker punch in La Liga against Barcelona in March, when the Catalans snatched a late win.

Ancelotti started an attacking side with Toni Kroos as the deepest midfielder and Eduardo Camavinga at left-back, as Los Blancos sought to overturn their narrow deficit.

Xavi, without Ousmane Dembele, Pedri, Frenkie de Jong and Andreas Christensen, stuck to the same formula that has served Barca well against Madrid in recent months, with four midfielders including Gavi, nominally starting on the left wing.

The game started at a furious pace and intensity, both teams keen to reach the final, but absolutely desperate not to be knocked out by the other.

Barcelona appealed furiously for a penalty in the first few minutes as David Alaba blocked Gavi's cross with his arm, but it was planted on the floor for balance.

The Austrian defender blocked Sergi Roberto's effort, while Vinicius and Ronald Araujo resumed their usual running battle at the other end.

Barca coach Xavi was booked for protesting a foul on Franck Kessie as tempers boiled over.

Thousands of Barcelona fans chanted Lionel Messi's name in the 10th minute, amid speculation he could leave Paris Saint-Germain, and they would have dearly loved some of the Argentine's magic.

Vinicius and Gavi were both shown yellow cards as they clashed, with referee Juan Martinez Munuera quick on the scene to try and calm things down.

- Lethal Madrid -

Los Blancos took the lead in stoppage time at the end of the first half, when they showed their prowess on the counter-attack.

Thibaut Courtois made a fine save to deny Robert Lewandowski and exactly 20 seconds later, Vinicius struck at the other end.

Rodrygo cut the ball back to the forward, who squeezed a shot home despite Jules Kounde's best attempt at a goal-line clearance. Benzema was on hand to make sure, but Vinicius's effort had already crossed the line.

The French forward soon was able to pounce though, finishing lethally from the edge of the box in an ocean of space after Luka Modric easily skipped away from Sergi Roberto.

Benzema slotted home his second from the penalty spot before the hour mark, sending Marc-Andre ter Stegen the wrong way after Kessie clumsily fouled Vinicius.

Xavi threw on Ansu Fati to try and spark a comeback of their own, but Barcelona could not find a way through.

It was one-way traffic as Ter Stegen denied Marco Asensio and then Benzema completed his hat-trick with a cool finish after a fine dribble and pass by Vinicius.

Madrid have lifted the trophy on 19 occasions, while their opponents Osasuna have never won it, securing passage to their second final after beating Athletic Bilbao on Tuesday.