This study examines the comprehensive effects of internal and external corporate governance mechanisms on the capital market response to corporate ESG reports. Based on a sample of 342 firm-year observations from the period 2016–2021, the study tested direct and bundling effects of internal governance and external assurance mechanisms on the capital market. The main empirical findings are as follows: (i) CEO duality, sustainability committee, and double assurance (third-party assurance with greenhouse gas emission certificate), have a direct and significant impact on cost of debt (negative) and Tobin_Q (positive); (ii) there are complementarities between the CEO duality and sustainability committee, Big4 assurance and the CEO duality, Big4 assurance and double assurance, enhancing the effect of debt financing. On the other hand, CEO duality and external assurance, as well as Big4 assurance and double assurance, show positive response in the capital market (Tobin_Q). However, the existence of a sustainability committee did not have a synergistic effect with any other variables. Finally, the combined effect of reliability enhancing mechanisms is slightly greater for companies issuing sustainability reports than for companies issuing integrated reports.