Premier Division
Siddal will contest the NCL Grand Final for a third-successive year after beating Thatto Heath Crusaders 36-22 at CWC Park on Saturday.
The reigning champions finished the year in top spot, but were on the ropes in the first half of this tie.
Siddal, who now haven't lost a league tie at home in two years, were 22-6 down at half time, but a stunning second-half turnaround saw them score 30 unanswered points to take their place in the Grand Final at Widnes on October 28.
Within just 11 minutes of the second half kicking off, Siddal were 24-22 up, before 37-year-old former Gloucestershire All Golds Head Coach Lee Greenwood scored late on to seal the tie - sparking rapturous celebrations.
In the top tier's other play-off tie, Rochdale Mayfield travelled to Wath Brow Hornets on Tuesday night, losing 24-18.
That result means Mayfield, 2016 Challenge Trophy winners, are out and their season comes to an end.
Thatto's second-placed finish in 2017 means they get a second chance at making the final - they host Wath Brow on Saturday to decide who will face Siddal in the showpiece event.
Division 1
Meanwhile, Normanton will take on either Milford Marlins or York Acorn in the Division 1 play-off final.
The Knights overcame Lock Lane 16-9 in the second tier's play-off semi-final, with Milford hosting Acorn in the other semi to decide who will follow them to Widnes in a clash for a place in the NCL Premier Division.
Division 2
Elsewhere, it's congratulations to Bradford Dudley Hill who have been promoted to NCL Division 1.
Hill were impressive on the road on Saturday, claiming a hard-earned 34-22 win at Wigan St Judes in the Division 2 promotion final to seal their spot in the second tier.
Division 3
Finally, Dewsbury Moor will go head-to-head with Woolston Rovers in the NCL Division 3 play-off final.
In the semis, The Moor beat Oldham St Annes 36-16 on Saturday, while Woolston Rovers picked up an impressive 24-20 win at Eastmoor Dragons.
Full details of the NCL finals double-header, taking place in Widnes on October 28, will be announced shortly.
