We establish a closed formula for a singular vector of weight λ´β in the Verma module of highest weight λ for Lie superalgebra glpm|nq when λ is atypical with respect to an odd positive root β. It is further shown that this vector is unique up to a scalar multiple, and it descends to a singular vector, again unique up to a scalar multiple, in the corresponding Kac module when both λ and λ´β are dominant integral.