A late rally was not enough for Pompey as they slipped to defeat at fellow promotion hopefuls Doncaster.
A goal in each half from Reece James and Fejiri Okenabirhie ensured Kenny Jackett's side had plenty of work to do.
The Blues improved as the contest progressed, with Ronan Curtis, Jack Whatmough and Harvey White all going close before John Marquis reduced the deficit in stoppage-time.