  In this paper we present a full set of 2- and 3-point functions for massless
QCD at three-loop order in the MSbar scheme. The vertex functions are evaluated
at the asymmetric point with one vanishing momentum. These results are used to
relate the MSbar coupling constant to that of various momentum subtraction
renormalization schemes at three-loop order. With the help of the known
four-loop MS-bar beta-function we then determine the four-loop coefficients of
the corresponding MOM beta-functions.
  As an application we consider the momentum dependence (running) of the
three-gluon asymmetrical vertex recently computed within the lattice approach
by Ph. Boucaud et al. (JHEP 04 006 (2000)). An account of the four-loop term in
the corresponding beta-function leads to a significant (around 30%) decrease of
the value of the non-perturbative power-suppressed correction to the running.
