Bristol were well in the game for the first 60 minutes, giving as good as they got, but they had no answer to the Knights who dominated the final quarter and delighted their Castle Park supporters by scoring three tries with some outstanding finishing and awesome defence on the two occasions the visitors threatened to score down their left flank.
Both sides started well but it was Bristol who had slightly the better of the early exchanges with winger Jack Tovey almost scoring before they eventually opened their account with a penalty by fly-half Adrian Jarvis
The Knights hit straight back with a Tristan Roberts penalty. Dougie Flockhart set up the first try, capitalising on an errant Bristol lineout to sprint ahead before feeding the supporting Latu Makaafi who powered his way over the remaining 40 metres. Bristol responded as Fatialofa made ground and fed the supporting Watkins who scored a try that Jarvis converted.
Back came the Knigths with Oli Goss and Stevie McColl setting up Flockhart to score in the corner. Roberts's excellent touchline conversion meant his side led 17-10 at the break.
Bristol's plan B after the restart was to drive the Knights pack back at every opportunity, but the hosts managed to withstand the pressure, even managing to stop a 50-metre attack down the left flank through flanker Neil Cochrane and scrum-half Chris Hallam.
All Bristol had to show for all their second-half territory was a penalty by Jarvis.
By now the Bristol pack was visibly tiring and it was the Knights who started to take the game by the scruff of the neck.
McColl set up replacement lock Dom Parsons who raced over for a try and then on 70 minutes the Knights claimd their bonus point try.
Knights' centre PJ Gidlow's inside pass released winger Matt Williams who evaded the sole defender to score a try that was converted by Roberts.
Ed Jackson then started and finished the fifth try from inside his own half, and with the help of Williams, who pulled up shy of the tryline with cramp.
A seventh win of the season moved Doncaster up to fifth.