In the 250th El Clasico, Real Madrid beat Barcelona and went top of the league.
After Vinicius Jr.'s shot was saved by Ter Stegen, Benzema scored Real's first goal.
The champion's lead was doubled before the half-time break.
Rodrygo settled the game with a penalty after Ferran Torres pulled one back.
The rivals started the day with seven wins and a draw from their first eight games, but Real are still perfect.
This was the first time in almost a year that Barcelona had lost an away game.
At the end of last season, Barcelona looked like they were on their way back to the top of Spanish football after beating Real Madrid.
They spent a lot of their future earnings on signing. It was hoped that it would lead to instant success and more earnings.
They showed how far behind their old rivals they are, despite facing early elimination from the European competition.
They are still within three points of the top spot, despite their first defeat of the season. Managers are not allowed to lose in this game.
Something for Xavi to think about is how they looked after they brought on young people.
Before those introductions, Barcelona was down and out. Fati's cross was turned into a goal by Fernando, who scored his second goal of the season.
Fati tried to grab a point with an acrobatic volley, but it went just wide before Rodrygo settled the game.
The Ballon d'Or is likely to be won by Benzema, who led Real Madrid to two titles last year.
He has had a slow start to the year. His goal was his fourth of the season.
The France international thought he had a fifth in the second half when he finished from outside the box, but he didn't hear the whistle go for an obstruction.
The man who was in top form before Sunday's game was Robert Lewandowski.
The two-time Best Fifa Men's Player netted nine goals in the first eight games of the season.
He wasn't able to finish Benzema this time. He slid a cross over an empty net and hit a free- kick into the wall.
The Pole will score a lot of goals this season, but Benzema showed he's still the best.