Tua Otto scored with the final play of the game at Doncaster to send Jersey through to the British and Irish Cup quarter-finals for the first time.
With the islanders on the brink of elimination, Samoan centre Otto darted through to touch down after earlier tries from Pierce Phillips and Gary Graham had kept hopes alive.
Michael Heaney's try helped put the hosts 13-3 up early in the second half.
Both sides will now face away ties in the next round.
Doncaster went into the game four points clear in Pool Five and already assured of a place in the last eight, while Jersey needed a win to guarantee qualification without having to rely on results elsewhere.
The first period, which was dominated by the battle at scrum time, finished 3-3, despite Jersey ending the half with 14 men, following Otto's yellow card for stopping the hosts from taking a quick penalty.
They made that advantage count soon after the break when scrum-half Heaney scored by the posts and Dougie Flockhart's penalty then gave Knights a ten-point margin.
With results in other groups not going Jersey's way, the islanders battled back with skipper Phillips powerfully finishing off a well-worked move to the cross the line.
A further Flockhart penalty made it 16-10, but the visitors led for the first time just after the hour mark when flanker Graham grounded from a catch-and-drive maul.
Lockhart continued his impressive form with the boot, edging the Knights ahead and potentially sending Jersey out.
In response, Otto almost snuck in at the corner for a try, but he was bundled into touch, before the outside centre crucially breached the Doncaster defence a minute from time to ensure his side would go through as one of the best placed runners-up in the group stage.
Despite the loss the Knights top Pool Five but, like Jersey, will be away in the quarter-finals to either Leinster A, Yorkshire Carnegie, Bedford Blues or Cornish Pirates.
Doncaster: Jarvis; Flockhart, Bulumakau, Clark, Lewis; Cusack, Heaney; List, Hunter, Quigley, Challinor, Hotson, Makaafi, Hills (capt), Stedman
Replacements: Veikoso, Sproston, Pasquali, Phelan, Shaw, Humberstone, Field.
Jersey: Adair; Howe, Otto, Cooke, Lane; Cope, Fisilau; Lockwood, Selway, Tomaszczyk, Rowlands, Phillips (capt), Freeman, Graham, Haining
Replacements: Lancuba, Garcia-Veiga, Kerrod, Kolo'ofa'i, Rae, Moates, Jennings