Relativistic one-component ab initio core model potentials are presented for first-, second-, and third-row transition elements; corresponding valence spaces comprise the ns, (n-1) d, and (n-1) p shells. Direct relativistic effects on the valence electrons are explicitly taken into account by using one-component relativistic kinetic energy and Douglas-Kroll transformed no-pair nuclear attraction interaction operators. The Coulombic part of the atomic core-valence interaction has been fitted to the corresponding all-electron mean-field operators whereas a matrix representation has been chosen for the exchange part. While not involved in the fitting process, all-electron orbital energies and radial expectation values of the valence orbitals are very well reproduced in atomic model potential calculations. Molecular test calculations have been performed on selected transition metal oxides. Employing a [4s, 4p, 4d] contraction of the valence basis, excellent agreement between core model potential and all-electron no-pair results is achieved for bond distances, harmonic frequencies, and dissociation energies.