The tribology of 2-methacryloyloxyethyl phosphorylcholine monolayers in water is studied using molecular dynamics simulations. Our results show two distinct shear regimes where the first is dominated by hydration lubrication, exhibiting near zero friction coefficients, and the second by chain-chain interactions, resembling monomer-supported lubrication. These results provide insight into the hydration lubrication mechanism - a phenomena thought to underlie the extremely efficient lubrication provided by surfaces functionalized with polyzwitterionic polymer brushes and the mammalian synovial joint.