Background: The COVID-19 pandemic resulted in drops in access to and availability of a number of evidence-based interventions (EBIs) known to reduce under-5 mortality (U5M) across a wide range of countries, including Rwanda. We aimed to understand the strategies and contextual factors associated with preventing or mitigating drops nationally and subnationally, and the extent to which previous efforts to reduce U5M supported the maintenance of healthcare delivery. Methods: We used a convergent mixed methods implementation science approach, guided by hybrid implementation research and resiliency frameworks. We triangulated data from three sources: desk review of available documents, existing routine data from the health management information system, and key informant interviews (KIIs). We analyzed quantitative data through scatter plots using interrupted time series analysis to describe changes in EBI access, uptake, and delivery. We used a Poisson regression model to estimate the impact of COVID-19 on health management information system indicators, adjusting for seasonality. We used thematic analysis of coded interviews to identify emerging patterns and themes. Results: We found moderate 4% (IRR = 0.96; 95%CI: 0.93, 1.00) and 5% (IRR = 0.95; 95%CI: 0.92, 0.99) drops in pentavalent and rotavirus 2 doses vaccines administered, respectively. Nationally, there was a 5% drop in facility-based delivery (IRR = 0.95; 95%CI: 0.92, 0.99). Lockdown and movement restrictions and community and health-worker fear of COVID-19 were barriers to service delivery early in the pandemic. Key implementation strategies to prevent or respond to EBI drops included leveraging community-based healthcare delivery, data use for decision-making, mentorship and supervision, and use of digital platform. Conclusions: While Rwanda had drops in some EBIs early in the pandemic, especially during the initial lockdown, this was rapidly identified, and response implemented. The resiliency of the health system was associated with the Rwandan health system's ability to learn and adapt, encouraging a flexible response to fit the situation.