The impacts of financial deepening on economic growth have been broadly discussed in the economic literature. Due to the recent financial crisis, its long-run effects must be carefully analyzed. This paper seeks to investigate the mechanism in which credit increases affect growth through the banking sector market structure. With enough competition in this market, the number of banks will be a good instrument for credit in a growth regression. Evidences of competition variability in the Brazilian banking sector are found at the local level as well as a non-linearity in bank entry at a specific market. Finally, after including this non-linear relationship in the growth regression’s first stage, it was found that, as expected, not only are the impacts of a credit increase positive but also that the identification strategy was well specified, since the positive effect of growth on credit was eliminated correctly.