With the final whistle set to blow, Bristol wing Tom Varndell picked a long pass by centre Jack Tovey off his bootlaces to deny Knights a first-ever double over the former Premiership side and secure his side a 31-29 win.
Bristol, who were playing their first game in three weeks, were the first to threaten but former Welsh international Gavin Henson was off target with an angled 40 metre penalty on three minutes.
Good handling saw wing David Lemi get away down the left flank but the cover nailed Tovey as soon as he received his inside pass.
Knights drew first blood as wing Tyson Lewis celebrated his 100th game for the club on ten minutes
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The home side went through a number of phases in midfield before moving the ball crisply out to their left flank where Lewis produced a good fend before sprinting in at the corner for an unconverted try.
Bristol found it hard to breach the Doncaster defence and it took them until the end of the first quarter to mount their first sustained period of pressure in the home 22.
But it didn’t bring them any joy – quite the contrary in fact – as an interception by wing Andy Bulumakau from Henson’s pass led to Doncaster extending their lead.
But for Bulumakau losing his balance he would have backed himself to run the 80 metres to score himself.
Realising he couldn’t go all the way he looked around for support on the halfway line and it was there in numbers with skipper Michael Clark twice involved in the handling move which ended with Lewis racing in for his second.
Declan Cusack added the conversion to make it 12-0.
Even at that stage, Bristol knew they had to score the next try and did that when flanker Olly Robinson touched down from a driving maul – a tactic Knights had used to good effect in their win at Ashton Gate in November – and Henson added the extras.
The visitors edged into the lead when scrum-half Will Cliff touched down for a second converted try after No 8 Mitch Eadie had been tackled just short.
Knights elected to go for a try rather than take on the kickable penalty just before half-time and their gamble paid off when prop WillGriiff John capped an impressive performance with a try under the posts which Cusack converted to make it 19-14.
Cusack extended the lead with a penalty after the break but Bristol called the shots for most of the third quarter and full-back Jack Wallace went over for their third try.
Good work in the build-up by Michael Heaney helped set up a converted try for second-rower Matt Challoner.
Cliff threw his side, who were trailing 29-19, a lifeline on 66 minutes when claiming his second try to set up a grandstand finish.
Doncaster Knights: McIlwaine, Bulumakau, Clark, Hurrell, Lewis; Cusack, Heaney; List, Hunter, John, Challinor, Phelan,Makaafi, Hills, Shaw. Rep:Veikoso, Sprotson, Armstrong, Cook, Young, Armitage, Field.
Bristol Rugby: Wallace, Varndell, Tovey, Carpenter, Lemi; Henson, Cliff; O’Connell, Jones, Perenise, Evans, Glynn, Mama, Robinson, Eade. Rep: Ross, McMulllen, Traynor, Cortes, Joyce, Smid, Roberts, Morgan.