A [Ni/Mg]-catalyzed orthogonal tandem polymerization has been developed starting from enol phosphates. Initial investigations conducted on branched 1,3-dienes as monomers enabled identification of a Mg-initiated polymerization process leading to 1,4-cis-polydienes. When aryl enol phosphates are used as monomers, the [Ni/Mg]-catalyzed tandem polymerization affords 1,4-cis-polydienes with selectivities up to 99%. Elastomeric or crystalline materials were obtained by simple structural modifications of the monomeric unit. This tandem approach appears as a straightforward and efficient way to enforce diversity and selectivity in diene polymerization while retaining a fair degree of control, just as observed for stepwise systems that are accessible through established time- and manpower-consuming synthetic procedures.