The refinement of Y2BaCuO5 (Y211) particles is a matter of significant importance in fabricating high-performance YBa2Cu3O7- (Y123) superconductor bulks by top-seeded melt growth (TSMG). However, coarsening and epitaxial growth naturally occur to the preexisting Y211 grains in the conventional process, causing an unwanted size enlargement. Here, for the first time, we report a novel TSMG approach in which instead of Y211, modified precursor powders (MPP, Y2O3, and Ba2Cu3Ox) were employed. As a result, massive numbers of Y211 nanoparticles were derived from the homogeneous nucleation catastrophe through peritectic solidification of Y2O3+Ba-x-Cu-y-OY211. Correspondingly, superior property of trapped field was achieved from the MPP-processed bulk.