Strong terahertz (THz) or mid-infrared (MIR) laser pulses offer the potential to coherently manipulate the properties of materials on ultrafast timescales, which has emerged as a viable approach to coherently engineer material on demand. However, these approaches have always been limited to picosecond timescale owing to the electronic and structural relaxation bottlenecks. Here, we demonstrate the femtosecond control of optical nonlinearity in a semiconductor ZnO crystal. Our scheme is realized by engineering the electron motion with a near-infrared (NIR) waveform-controlled two-color pulse and a polarization-skewed pulse. The pump-probe methodology of second-harmonic generation (SHG) reveals the connection between the optical nonlinearity modulation and the ultrafast electron dynamics. Our work provides new freedom for rationally designing the structure and transient symmetry of crystals with light and paves the way for petahertz (PHz) high-speed signal processing technologies.