The reaction e+p --> e+pi+n at CM energy W=1125 MeV and momentum transfer Q^2=0.117 GeV^2 has been measured. The transverse and longitudinal structure functions have been separated by varying the polarization of the virtual photon (Rosenbluth plot) with a 3 to 4% error. In addition the longitudinal- transverse interference term has been determined measuring the left-right asymmetry with an accuracy of 3%. The experimental data are compared to model calculations, and the sensitivity of the results to the axial and pion form factors is discussed.