Ronaldo's 85th-minute strike saw Madrid claim their 13th successive away LaLiga win, surpassing the mark of 12 set by Pep Guardiola's Barca side from May 2010 to January 2011.
The goal was Ronaldo's first of the league campaign, the Portuguese having drawn a blank in his three previous LaLiga appearances.
In contrast to his reputation as one of the world's most ruthless forwards, Ronaldo needed 28 shots to break his duck, with just seven of those efforts hitting the target.