A golf ball includes a thermoplastic inner core and a thermoset outer core layer. The inner core has a surface hardness of about 40 to 80 Shore C and a center hardness of about 30 to 75 Shore C, the center hardness being less than the surface hardness to define a first positive hardness gradient. The cover includes an inner cover layer and an outer cover layer. The thermoplastic inner core comprises a highly-neutralized ionomer including an acid copolymer of ethylene and an α,β-unsaturated carboxylic acid; a plasticizer; an organic acid or salt thereof; and a cation source present in an amount sufficient to neutralize from about 70 to 100% of the acid groups present. The outer core layer includes a polybutadiene rubber and has a surface hardness greater than an interior hardness to define a positive hardness gradient of less than about 25 Shore C.