Carbon-encapsulated crystalline boron nanopowder and coarse magnesium powder are used as inexpensive tailored starting materials for the fabrication of high-performance MgB2 superconducting wire. A low sintering temperature leads to a high critical current density, as a result of nanometer-sized boron powder, surface oxidation preclusion by carbon encapsulation, and grain alignment by elongated magnesium coarse powder.