Away goals from David Villa and Lionel Messi left Barca the happier of the teams, after Real had created better chances, and their night was crowned with news that Spain midfielder Cesc Fabregas had finally agreed his move from Arsenal.
Real had taken the lead through Mesut Ozil after only 13 minutes in a vibrant atmosphere, and Xabi Alonso grabbed the equaliser early in the second half.
The second leg is at the Nou Camp on Wednesday.
"We are behind with our preparations so it has been a huge achievement to get a result against a Real Madrid side who have played very well," Barca coach Pep Guardiola told reporters.
Referring to Fabregas he said: "Cesc grew up in Barcelona he became a huge player thanks to Mr [Arsene] Wenger and Arsenal, and now he is a better player than we he left. Now we will try and make him better."
Barca gave new signing Alexis Sanchez his debut in an unfamiliar line-up that also included 20-year-old midfielder Thiago Alcantara in place of Xavi.
In the absence of Carles Puyol and Gerard Pique, both suffering with injuries, Javier Mascherano and Eric Abidal teamed up in the centre of Barca´s defence, where they were quickly found out.
Karim Benzema, who has scored eight for Real during the pre-season, beat Abidal on the edge of the area and squared for the advancing Ozil to slot past Victor Valdes.
VILLA SHOT
Penned back in their area, Barca struggled to mount a single shot until the 35th when Messi fed Villa wide on the left.
The Spanish striker cut inside Sergio Ramos and from the edge of the area curled a shot over Iker Casillas and into the top corner.
On the stroke of half-time Barca hit Real with another sucker punch.
Messi scampered away toward the area, and as white bodies converged on him a lucky deflection saw him emerge unmarked into the area to slide the ball underneath Casillas.
Real lifted their game again after the break and when Alonso drilled a low shot in the corner, Barca were once again on the rack.
With the memories of last season's bad-tempered clashes in the league, King's Cup and Champions League still fresh in mind tempers started to flare, adding extra spice to the atmosphere, but Real failed to capitalise on their chances.
Pep Guardiola sought to tighten up his side introducing Xavi and Pique, and he successfully defended his unbeaten record as coach at the Bernabeu.
Mourinho sent his number two Aitor Karanka out to speak to reporters:
"Perhaps we didn't get the result we deserved but we are happy with the work of the team," Karanka said.
"It's a bittersweet result, but we showed we are a better team than last year."
