The unsteady evolution of microscale breaking waves induced by a free-surface drift layer is studied by performing a large-wave simulation (LWS) of the corresponding free-surface flow. The initial flow condition is the superposition of a gravity wave and the surface layer. Their interaction models the propagation and breaking of gravity waves in the ocean under the influence of wind forcing. The governing Euler equations are filtered according to the LWS formulation and solved numerically by a spectral method for the spatial discretization and a fractional time-step scheme for the time advancement. Lengths are rendered dimensionless by the drift-layer thickness and velocities by the gravity-wave celerity. The flow depends on the Froude (gravity), Fr, and Weber (surface tension), We, numbers, through the dynamic free-surface condition, the initial surface drift velocity, q, and the initial wave height, H ∘, which sets the breaker intensity. Several cases are considered for Fr = 3.6, We = ∞, 10 and 5, q = 0.3, and H ∘ = 5.2, 6.5 and 7.8. The results, associated with microscale breakers, focus on the free-surface profile evolution and the subsurface unsteady flow characteristics. Decreasing the Weber number results in the reduction of the breaking crest elevation, the growth of the breaker bulge size and the lowering of the breaker toe elevation, while increasing the initial wave height results in stronger breakers and the increase of the surface tension influence. The free-surface acquires its steepest slope at the spilling face of the breaker, upstream of the toe, at start of breaking; this value is not affected by surface tension. The fluid streamwise velocity acquires its maximum magnitude at the crest of the breaker during breaking and after the occurrence of maximum surface slope. The time interval between the two events is equal to about three quarters of the wave period for the weaker breaker ( H ∘ = 5.2) and decreases to zero for the stronger breaker ( H ∘ = 7.8). The maximum crest fluid velocity becomes equal to the initial wave celerity C for We = ∞, but acquires smaller values for finite Weber numbers, which decrease with decreasing Weber number and decreasing initial wave height, i.e., it becomes equal to 0.92 C for We = 5 and H ∘ = 5.2. The speed of the breaker crest, on the other hand, acquires values that are larger than C and increase with increasing initial wave height but not affected by surface tension. In all cases, during post breaking, the crest fluid velocity is always much smaller than the wave celerity and in agreement with experimental measurements. The wave energy dissipation increases during breaking and becomes maximum at about the same time the crest fluid velocity becomes maximum. Finally, a vortex, which disrupts the vorticity field of the surface layer, is formed in the spilling region of the breaker, and its peak strength increases with decreasing Weber number. The disruption of the surface layer is stronger for the weak breakers and weaker for the strong ones.