In the present study, we determined the coefficient of friction (COF) values of lubricated moving metal-fixed polymer and lubricated moving polymer-fixed metal tribo-pairs. The metal of stainless steel (304) and the polymer of polytetrafluoroethylene (PTFE) lubricated with poly-alpha-olefin (PAO6) base oil, 32# hydraulic oil (32#HO) or 15# aviation hydraulic oil (15#AHO) were tested on a standard ball-on-three plates (BTP) test machine. The tribo-pairs exhibited markedly different lubrication behaviors. For instance, the COF of a 304-PTFE tribo-pair (0.008) comprising a moving 304 ball and three fixed PTFE plates was approximately 3.5 times lower than that of a comparable PTFE-304 tribo-pair with the same lubricants under the same working conditions. The anomalous lubrication behavior was ascribed to the interfacial slip simulated by COMSOL Multiphysics software package to demonstrate the experimental results. The results indicated that interfacial slip is a key property of the materials used in the mechanical structures to decrease friction and wear, and increase the service life of tribo-pairs used in applications such as artificial joint replacements and pressure vessel seals.