A method of laser spot welding a workpiece stack-up (10) that includes at least two overlapping steel workpieces (12, 14, 150) is disclosed. The method includes directing a plurality of laser beams (24, 24′, 24″) at the top surface (20) of the workpiece stack-up to create a molten steel weld pool (92) that penetrates into the stack-up. The molten steel weld pool is then grown to penetrate further into the stack-up by increasing an overall combined irradiance of the laser beams while reducing the total projected sectional area (88) of the laser beams at a plane of the top surface of the workpiece stack-up. Increasing the overall combined irradiance of the laser beams may be accomplished by moving the focal points (66, 66′, 66″) of the laser beams closer to the top surface or by reducing the mean angle of incidence (86) of the laser beams so as to reduce the eccentricity of the individual projected sectional areas of the laser beams.