An axisymmetric frictionless adhesive contact problem for a spherical indenter pressed against an isotropic elastic incompressible half-space under equibiaxial stretching is studied in the framework of the generalized Johnson-Kendall-Roberts (JKR) theory, which accounts for the effect of weak coupling between fracture modes I and II by means of a phenomenological mode-mixity function. The model predicts that contact area can withstand a larger level of the substrate stretch under moderate pre-pulling force. We have provided simple formulas to evaluate the pull-off force and the critical contact radius at the detachment point.