Catalyzes the NADPH-dependent reduction of ketopantoate into pantoic acid. Has a strong preference for NADPH over NADH as the electron acceptor. Pantoate, ketoisovalerate, oxaloacetate, pyruvate, 3-hydroxypyruvate, alpha-ketoglutarate, alpha-ketobutyrate, and acetaldehyde cannot serve as substrates for reduction. (R)-pantoate + NADP(+) = 2-dehydropantoate + H(+) + NADPH Optimum pH is 6.25. Optimum temperature is 42 degrees Celsius. Cofactor biosynthesis; (R)-pantothenate biosynthesis; (R)-pantoate from 3-methyl-2-oxobutanoate: step 2/2. Monomer. Belongs to the ketopantoate reductase family.