Ni-catalyzed single-crystal TiO2 nanowire growth was observed to occur well below the bulk Ni melting point when a small amount of P was present. TEM, SAED, EDXS, and EELS analyses as well as consideration of the Ni/P phase diagram point to a previously unreported mechanism of nanowire growth catalyzed by a liquid Ni/P eutectic shell surrounding a solid Ni core. High-resolution elemental analysis supports the conclusion that the active catalyst is the outer liquid Ni/P layer with P present at a 3-8% level surrounding a solid Ni core. Growth proceeds by precursor adsorption onto the liquid layer followed by diffusion to the growing surface of the nanowire. This catalyst system produces rutile TiO2 nanowires efficiently. We believe that the technique is generalizable to other metal/dopant systems which could lead to the synthesis of other hard-to-synthesize nanowires.