We consider a late closed universe of which scale factor is a power function of time using observational data from combined WMAP5+BAO+SNIa dataset and WMAP5 dataset .
The WMAP5 data give power-law exponent , \alpha = 1.01 agreeing with the previous study of H ( z ) data while combined data gives \alpha = 0.985 .
Considering a scalar field dark energy and dust fluid evolving in the power-law universe , we find field potential , field solution and equation of state parameters .
Decaying from dark matter into dark energy is allowed in addition to the non-interaction case .
Time scale characterizing domination of the kinematic expansion terms over the dust and curvature terms in the scalar field potential are found to be approximately 5.3 to 5.5 Gyr .
The interaction affects in slightly lowering the height of scalar potential and slightly shifting potential curves rightwards to later time .
Mass potential function of the interacting Lagrangian term is found to be exponentially decay function .