Bristol led 10-6 at half time but were then swept aside as Castleford countered through Luke Franks (2), Alex Hall (2), Declan Walker and Matt Lawtey to take a 12-10 lead.
At the start of the final period, Bristol hit back to trail 12-11. But goals by Hall and Lawtey – his fifth of the game – saw Castleford home.
Cheltenham Spartans also enjoyed the third period against Durham Palatinates, scoring seven through Rob Parker and juniors Taylor Walsh (2), George Glover and Dan Day before winning 18-11.
Andrei Delikatny (4) and Matt Helps (3) were the chief marksmen in Croydon’s 13-8 defeat of Birmingham. Ben Naish's third goal 55 seconds from the end put Hucknall 8-7 up against Worthing only for Ben Curtis to equalise from a man-up chance with 17 seconds left.
Photo (Trevor Hyde): Five-goal Matt Lawtey in action at Habersdashers.