The Frenchman has now entered the history books of the Clasico while also leading Los Blancos to the final of the Copa del Rey against Osasuna.
When Camp Nou was chanting for Lionel Messi (35) in the 10th minute, Benzema appeared.
Camp Nou was crying out for the presence of an elite footballer, someone who had the ability to change a game, to define matches even when the opponent is dominating.
The wishes of the fans were granted only not quite as they wanted. Benzema, coming off the back of a hat-trick against Real Valladolid on Sunday, completed a colossal performance and exposed Barcelona's tactical shortcomings in the process.
"Karim is so important for us. He is back. Both in the game against Valladolid and today he was decisive as he so often is," said manager Carlo Ancelotti after the game.
The French striker took command in Real's front line. First, by dragging the markers away and then, by inciting dangerous moves. He played a part in Vinicius' 45th-minute goal and, in the end, scored a hat-trick that overwhelmed Xavi's team.
"The second goal penalised us a lot. The penalty too... details. We didn't take advantage of our moments and, as I said in the press conference, Madrid were always favourites. They are the Champions League winners, a great team," said the Catalan coach.
Benzema is only the second player to score a hat-trick in a Clasico at Camp Nou while wearing the Real Madrid shirt. Ferenc Puskas, on 27 January 1963, was the first striker to do so.
On the eighth matchday of LaLiga that season, the iconic Hungarian striker scored (24', 35' and 71') on three occasions to silence the stands at the Estadio Cule. Alfredo Di Stefano (47') and Gento (67') rounded off the rout for Madrid in that game while Re (34') provided the only goal for Barcelona.
Ancelotti warned on Sunday that in April "the real season begins". At least the Italian has Benzema back in full flight after an injury-plagued season.