Pompey dropped to 10th in the League One standings after suffering a narrow defeat to Doncaster.
Jack Whatmough and Marcus Harness both had shots saved for the Blues, but neither side created much at Fratton Park.
Rovers snatched all three points in the closing stages, however, when Reece James found space to curl the ball home.
Fans can watch the key moments (top video) or register on iFollow to see extended highlights (middle video) and a full match replay (bottom video).