Reduces achiral isoflavones to chiral isoflavanones during the biosynthesis of chiral pterocarpan phytoalexins (PubMed:28394400). The reduction product is a third isomer, which represents the penultimate intermediate in the synthesis of the phytoalexin (-)-medicarpin, the major phytoalexin in soybean (PubMed:28394400). (3R)-vestitone + NADP(+) = 2'-hydroxyformononetin + 2 H(+) + NADPH