But van Nistelrooy's equaliser - his second of the match after Diego Milito had twice put Zaragoza in front - combined with a late Espanyol leveller means Madrid still hold the upper hand heading into the final round of fixtures.
Real coach Fabio Capello insisted afterwards: "The Liga still isn't won.
"In the first-half we were disorganised. But in the second we recovered the result by showing at all times desire, heart and team spirit.
"I'm happy with the final result and all the lads in the dressing room are also."