We report the first reconstruction in hadron collisions of the suppressed decays B−→D(→K+π−)K− and B−→D(→K+π−)π−, sensitive to the Cabibbo-Kobayashi-Maskawa phase γ, using data from 7  fb−1 of integrated luminosity collected by the CDF II detector at the Tevatron collider. We reconstruct a signal for the B−→D(→K+π−)K− suppressed mode with a significance of 3.2 standard deviations, and measure the ratios of the suppressed to favored branching fractions R(K)=[22.0±8.6(stat)±2.6(syst)]×10−3, R+(K)=[42.6±13.7(stat)±2.8(syst)]×10−3, R−(K)=[3.8±10.3(stat)±2.7(syst)]×10−3 as well as the direct CP-violating asymmetry A(K)=−0.82±0.44(stat)±0.09(syst) of this mode. Corresponding quantities for B−→D(→K+π−)π− decay are also reported.