But Real were soon level as Ronaldo fired home before halftime.
Angel Di Maria's cross from the left, having switched wings with Ronaldo, found the Portuguese who seemed to hang in the air to steer the ball past United goalkeeper David De Gea. Ronaldo kept his celebrations muted in respect to United's away fans.
It was tough on De Gea who had previously tipped Fabio Coentrao's drive onto a post.
In the second-half, Robin van Persie had two glorious chances to put United ahead, hitting the crossbar before scuffing his shot and seeing it cleared off the line with Real keeper Diego Lopez beaten.
While Real dominated possession, United will come away delighted with their performance and feeling they should have won.