CC10 at ${cal O}(alpha_s )$: QCD corrections to $e^+ e^- to mu^- bar u_mu u bar d$ at LEP2 and the Next Linear Collider

QCD one-loop corrections to the semileptonic process $e^+ e^- to mu^- bar u_mu u bar d$ are computed. We compare the exact calculation with a ``naive approach to strong radiative corrections which has been widely used in the literature and discuss the phenomenological relevance of QCD contributions for LEP2 and NLC physics.