Despite the ability of sorghum [Sorghum bicolor (L.) Moench] to withstand harsh environmental conditions, it is susceptible to water-deficit stress during grain filling. To identify post-flowering drought tolerant sorghum genotypes, parents of nested association mapping populations were evaluated under controlled and water-deficit conditions in greenhouse and field conditions. In both experiments, water-deficit stress was imposed by withholding water during the grain-filling period.In field experiments, rootzone soil moisture was measured weekly using a neutron probe to quantify the plant available water under well-watered and water-deficit conditions. Investigations were focused on determining the variability in the grain-filling pattern across different positions within the panicles (intra-panicle) of 11 different sorghum genotypes. Water-deficit conditions characterized by low plant available water had a consistently negative association with grain number along different positions in the panicle. Our findings indicate that maintaining grain numbers per panicle under post-flowering water deficit is more important than increasing individual grain weight. Among the tested genotypes, SC35 and SC1103 were most tolerant to water-deficit conditions under greenhouse and field conditions, respectively. Currently available biparental populations, developed using these genotypes, provide an opportunity to enhance tolerance to post-flowering water-deficit stress in sorghum.