Opposition parties in electoral autocracies are marginalized and lack opportunities for office-holding with meaningful responsibilities. This makes it hard for them to convince voters to switch from ‘the devil they know’. As such, prevailing explanations of regime durability are based primarily on characteristics of ruling party. When opposition parties win, it is reactive not proactive. I contend that this understanding exists because we overly focus on opposition office-holding at the centre like legislative and cabinet seats. In this study, I propose that local politics has important and overlooked role in shaping the long-term prospects of opposition parties and hence regime durability. I contend that opposition local control, opposition leadership of local governments, is a way opposition parties can threaten authoritarian regimes. When the regime loses local elections, opposition parties gain control of local institutions which gives them unprecedented autonomy over state capacity and resources. This allows opposition parties to build their credibility through service delivery and good performance. I therefore argue that opposition control weakens the regime's hold on power because it makes it easier for opposition parties to proactively win support by providing them with a record in government. In this article, I use qualitative and quantitative evidence from Tanzania to demonstrate that opposition parties invest in local state capacity and improve the quality of public services to proactively build up their credibility. I then draw on electoral data to show that patterns of opposition local control can explain the long-term development of opposition support in Tanzania.