We present the partial branching fraction for inclusive charmless semileptonic B decays and the corresponding value of the Cabibbo-Kobayashi-Maskawa matrix element vertical bar V-ub vertical bar, using a multivariate analysis method to access similar to 90% of the B -> X(u)l nu phase space. This approach dramatically reduces the theoretical uncertainties from the b-quark mass and nonperturbative QCD compared to all previous inclusive measurements. The results are based on a sample of 657 X 10(6) B (B) over bar pairs collected with the Belle detector. We find that Delta B(B -> X(u)l nu; p(l)*(B) > 1.0 GeV/c) = 1.963X(1 +/- 0.088(stat) +/- 0.081(syst)) X 10(-3). Corresponding values of vertical bar V-ub vertical bar are extracted using several theoretical calculations.