Burnley's 1-0 victory over Blackpool earlier this evening means that the Rams need to win at the Keepmoat Stadium to stand any chance of securing an unlikely top-two finish and a return to the Premier League.
Things nearly started disastrously for Steve McLaren's men when Lee Grant slipped while trying to collect Richard Keogh's back-pass, only to recover quickly enough to stop the ball before the goalline.
This is also an important match for Doncaster, though, with Paul Dickov's side in need of wins to take them clear of the relegation zone, which currently sits three places and three points below them.
They were largely forced to play on the counter-attack, but had probably the best opportunity of an opening 40 minutes in which chances were few and far between, with Chris Brown going close.
Just as it appeared as though Doncaster would make it to the interval with deserved parity, Thorne's measured strike, following a layoff from Will Hughes, found the bottom corner in stoppage time.
It is the midfielder's first goal for Derby since joining on loan from West Bromwich Albion.