Titans pay for errors
Andre Bester's side led 15-14 at the break after a solid opening 40 minutes, Doncaster scoring two tries after Jonny Hampsey twice fumbled high kicks.
But the Knights knocked seven bells out of the Clifton Lane side to make it three wins from four in games against the sides this year. Doncaster ran in another four tries.
Said coach Bester: "We were on top in the first half but gave away two silly tries. Had we been further ahead, as we should have been, then it might have been different in the second half."
Titans, with five straight defeats in their play-off games, wrap up their season at Bedford on Saturday.