Clive Griffiths’ side scored seven tries as they destroyed the only side who could mathematically catch rampant leaders.
Whatever happens, the South Yorkshire club will certainly receive a warm welcome from Bristol fans when they head there on Friday for their penultimate game of this Championship season.
On Saturday, Doncaster got off to a confident start when ex-Rotherham Titans centre Lloyd Hayes crossed inside just two minutes and full-back Cameron Cowell quickly added their second.
Ealing scrum-half Luke Carter responded but Andy Bulumakau scored the first of his brace to put Knights in control, Dougie Flockhart slotting the first three of his six conversions for a 21-7 score at the break.
Fijian centre Bulumakau added his second try soon after the restart and, though Ealing winger James Cordy-Redden kept them in the contest, Knights flanker Jam Ram crossed just before the hour to leave his side on the verge of victory.
Charlie Foley, playing at fly-half, was next to score and – after a Flockhart penalty – replacement hooker Curtis Langdon also crossed.
By that point, Cordy-Redden had bagged his brace but the visitors had been utterly outplayed.
Doncaster were dominant up front, showing real edge in the set-piece while proving clinical in possession.
With their defence generally holding firm, too, it was a fine display against a top side.