The energies of the excited states in very neutron-rich ⁴²Si and ^41,43P have been measured using in-beam gamma-ray spectroscopy from the fragmentation of secondary beams of ^42,44S at 39A MeV. The low 2⁺ energy of ⁴²Si, 770(19) keV, together with the level schemes of ^41,43P, provides evidence for the disappearance of the Z=14 and N=28 spherical shell closures, which is ascribed mainly to the action of proton-neutron tensor forces. New shell model calculations indicate that ⁴²Si is best described as a well-deformed oblate rotor.