  The emergence of negative longitudinal magnetoresistance in the topologically
non-trivial transition-metal dichalcogenide PtSe$_2$ is studied. Low $T$/high
$\mu_0 H$ transport is performed for arbitrary field directions, and an
analytical framework is established. The source of the negative longitudinal
magnetoresistance is identified as the Kondo effect stemming from Pt-vacancies
contributing an uncompensated spin, exclusively at the sample surface. The
concentration of vacancies and the sample thickness are identified as tuning
parameters. The findings are substantiated by density functional theory, which
corroborates the proposed Pt-vacancy model.
