Champions Barca and second-placed Real were missing key players, with Lionel Messi out of the Catalan derby due to an ankle sprain and the suspended Cristiano Ronaldo and injured Kaka absent for the Valencia clash.
After a tight first half at the Mestalla, Real's Argentina striker Higuain broke the deadlock in the 54th minute with a header from Karim Benzema's cross before league top scorer David Villa equalised with his 12th of the season on the hour.
"It was a very important victory against one of our direct rivals," Higuain said in a television interview.
Higuain's Argentina team mate Messi was injured in Wednesday's Champions League victory at Dynamo Kiev, but was in the Nou Camp earlier on Saturday to show the fans the Ballon d'Or award he won this month.
His replacement, Pedro, fluffed a chance to put Barca ahead in the 14th minute when he robbed Francisco Chica but skewed his shot wide with Carlos Kameni's goal at his mercy.
Victor Valdes had to be alert to keep out Joan Verdu's dipping strike seconds later before Kameni acrobatically palmed away Thierry Henry's low effort.
Espanyol put up more of a fight in a scrappy second half but were unable to find an equaliser and Ibrahimovic and Gerard Pique went close to doubling Barca's lead.
"We knew it was going to be tough," coach Pep Guardiola told a news conference. "We played a very good first half but the reward was scant."
They are bidding for a sixth trophy to go with their Spanish and European Champions League titles, the King's Cup and the Spanish and European Super Cups.
"Results are indisputable because they are not a matter of opinion and definitively condition decisions," Zaragoza president Eduardo Bandres said at a news conference. "The statistics are extremely bad."
Supporters at the Romareda had earlier unfurled a banner saying "These fans don't deserve such humiliation," and the defeat left Zaragoza just above the relegation zon
