Forward Freddie Lockwood, who scored on his 50th appearance in the Falcons’ 33-12 win at Caldy in their competition opener eight days earlier, ensured a bonus point just before half-time, with Brett Connon converting for a fourth time.
Doncaster, who replaced Jordan Olowofela with Maliq Holden because of illness before kick-off, replied when substitute Euan McVie was fed by Morgan Strong shortly after coming on before Russell Bennett added the extras in the 52nd minute.
After Fletcher was sin-binned for killing a ruck, Tom Currie’s try and Bennett’s conversion meant a Connon penalty from 30 metres was a source of relief for Newcastle.
The hosts had to hold on during a nervy finale after Connor Edwards charged over from 20 metres and Telusa Veainu darted in to add Knights’ fourth try. Bennett converting both to reduce the deficit to three for the final eight minutes.
Knights had pushed Sale Sharks hard in a 43-37 away defeat on 1 November, but have now lost both of their Pool A matches as part of a four-game losing run.
