In injection moulding, high pressure is required to fill the mould, due to the viscosity of thermoplastic polymers, the reduced thickness of the cavity and the low mould temperature. Significant pressure reduction could be achieved by inducing the slip of the polymer melt over the mould surface, which occurs within the first monolayer of macromolecular chains adsorbed at the wall. Low surface energy coatings can suppress polymer adsorption and promote slip, but they have limited longevity. Laser ablation has been recently used to affect the slip of polymer melts by varying the surface roughness. However, all the proposed micro/nano-patterned surfaces resulted in a decrease of wall slip and a consequent raise of injection pressure. In this work, the effect of Laser-Induced Periodic Surface Structures (LIPSS) on the driving of the slipping of polyethylene terephthalate (PET) was investigated. Moreover, different orientation of the ripples (i.e. parallel and transversal to the polymer flow front) were analyzed. The results show that LIPSS have the remarkable capability of reducing the injection pressure up to more than 20% under standard injection moulding conditions. Ripples parallel to the polymer flow were observed to promote slip of polymer melts, due to reduced adsorption properties of the mould surface. Conversely, perpendicular ripples hinder the orientation of adsorbed chain loops towards the flow direction, increasing the entanglement density between adsorbed and bulk chains. Moreover, the results demonstrate how LIPSS can be used in injection molding to significantly decrease the filling pressure, without worsening the surface finish of moulded parts. They can also be used to control the filling flow pattern by selectively design parallel and perpendicular ripples as flow leaders and deflectors, respectively.