Both sides had a man sent off in the closing stages, with Espanyol looking set for a first league victory over Barca in 16 years before De Jong turned in Adama Traore's cross to salvage a point.
Xavi Hernandez's side moved back into the fourth and final Champions League spot as a result, level on 39 points with Atletico Madrid.
"A positive point in the end. We had good moments in both halves. Espanyol created very little but they were more clinical. It was an intense game. Real Madrid have already lost here this season. We could have won if we took our chances," Xavi said. "We could also have lost in the end but that would have been unfair. We're still in the fight for the Champions League and we have to keep battling."
Ferran Torres and Traore both went close for the visitors but they were pegged back on the stroke of halftime as Sergi Darder curled an effort in from the edge of the box after good work from Raul de Tomas.
Darder then returned the favour as he sent De Tomas away with a ball over the top that had looked to have won the game for the hosts.
Tempers flared late on as Gerard Pique and Nico Melamed both saw red following a coming together off the ball before De Jong's late effort saw the spoils shared.
"Luuk de Jong is an example and I say that in front of the whole squad. He's a top professional. He's a goal scorer and that's why we brought him on. He's had two chances and then scored another one," Xavi added.