Given a flat Higgs vector bundle (E, ∇, ϕ) over a compact connected special affine manifold, we first construct a natural filtration of E, compatible with both ∇ and ϕ, such that the successive quotients are polystable flat Higgs vector bundles. This is done by combining the Harder-Narasimhan filtration and the socle filtration that we construct. Using this filtration, we construct a smooth Hermitian metric h on E and a smooth one-parameter family {A t } t∈R of C ∞ automorphisms of E with the following property. Let ∇ t and ϕ t be the flat connection and flat Higgs field, respectively, on E constructed from ∇ and ϕ using the automorphism A t . If θ t denotes the extended connection form on E associated to the triple h, ∇ t and ϕ t , then as t −→ +∞, the connection form θ t converges in the C ∞ Fréchet topology to the extended connection form θ on E given by the affine Yang-Mills-Higgs metrics on the polystable quotients of the successive terms in the above mentioned filtration. In particular, as t −→ +∞, the curvature of θ t converges in the C ∞ Fréchet topology to the curvature of θ.