Opposition forces in electoral authoritarian regimes frequently protest against electoral manipulation with varying degrees of success. Why are opposition forces in some countries able to turnout the masses and successfully pressure a dominant regime to allow for electoral reform, whereas those in other countries exhibit much less success? This article argues that the cognitive complexity of electoral manipulation and the form of opposition organization explain divergent contestation and reform trajectories. Where the complexity of electoral manipulation is high, opposition forces are demobilized. Where the complexity of electoral manipulation is low, opposition forces may potentially mobilize the masses to protest for reform. Subsequently, the type of electoral reform – technocratic or partisan – pivots on whether opposition power is concentrated in one veto player or dispersed among multiple actors. I test the arguments through a controlled comparison of electoral reform in three Southeast Asian electoral authoritarian regimes – Singapore, Malaysia, and Cambodia.