The Krylov-Safonov theorem says that solutions to non-divergence uniformly elliptic equations with rough coefficients are Hölder continuous. The proof combines a basic measure estimate with delicate localization and covering arguments. Here we give a "global" proof based on convex analysis that avoids the localization and covering arguments. As an application of the technique we prove a W 2, ǫ estimate where ǫ decays with the ellipticity ratio of the coefficients at a rate that improves previous results, and is optimal in two dimensions.