Enhancing the dynamic asymmetry between liquid like and solid-like components leads to spontaneous segregation. As a typical example, the binary blends of stretched and free guest polymers were investigated by our dynamic Monte Carlo simulations. The results evidenced an entropic driving force for the strain-induced segregation between two components, similar to that for Onsager's lyotropic liquid crystals. In addition, with the decrease of strain rates, its competition with strain-induced crystal nucleation results in variable compositions in crystal precursors. The scenario helps to settle down the controversial arguments on the flow-induced precursors of shish-kebab crystallites in the melt.