Absolute cross sections have been determined following single neutron knockout reactions from 10Be and 10C at intermediate energy. Nucleon density distributions and bound-state wave function overlaps obtained from both variational Monte Carlo (VMC) and no core shell model (NCSM) ab initio calculations have been incorporated into the theoretical description of knockout reactions. Comparison to experimental cross sections demonstrates that the VMC approach, with the inclusion of 3-body forces, provides the best overall agreement while the NCSM and conventional shell-model calculations both overpredict the cross sections by 20% to 30% for 10Be and by 40% to 50% for 10C, respectively. This study gains new insight into the importance of 3-body forces and continuum effects in light nuclei and provides a sensitive technique to assess the accuracy of ab initio calculations for describing these effects.