The Tertiary reactivation of the Paleozoic basement in NE Sardinia is shown to reflect transtensional back‐arc tectonics, related to the western Mediterranean subduction rollback. During the Algéro‐Provençal basin opening, the left‐lateral Nuoro Fault, which is the prevailing structure in central Sardinia, operated as radial transfer between the west Sardinian rift and northern Tyrrhenian basin. Subsequently, it contributed to a tension gash‐like opening of the southern Tyrrhenian basin as conjugate fault to a right‐lateral fault set in SE Sardinia. Resulting antithetic rotations with respect to the arc are revealed by reoriented dikes in the basement. The tension gash‐like opening of the southern Tyrrhenian basin determined the gulf shape of the east Sardinian margin and the arc shape of its Calabrian counterpart. This structural control on the southern Tyrrhenian rollback scenario suggests that tension gash‐like opening of back‐arc basins represents an intrinsic aspect of subduction rollback.