Castleford: (16) 27
Tries: Dyer, McGoldrick, Lupton, Manu, Fletcher
Goals: Brough 3
Drop: Sculthorpe
Harlequins: (12) 12
Tries: Sykes, Williams
Goals: Sykes 2
Castleford took a major step towards retaining their Super League status with victory over Harlequins.
The Tigers began strongly with Luke Dyer and Ryan McGoldrick both going over for tries.
Paul Sykes and Danny Williams got Quins back into the game before Peter Lupton went over just on half-time.
But second-half tries from Willie Manu and Adam Fletcher helped edge the Tigers in front and their defence held firm for the win.
Castleford coach Terry Matterson "Everyone was telling us we were going to make the play-off semi-finals a few weeks ago.
"I never entertained that thought and the way Wakefield pushed St Helens last night shows it's not over.
"I don't usually show a lot of emotion but it's been a really tough month but the boys did me proud."
Harlequins coach Brian McDermott "I thought Cas played pretty well with a lot of emotion and had a lot of momentum in the first half.
"We allowed them to play too well and when they get a bit of momentum they can be a useful side.
"I believe we had momentum just before half-time after being starved of the ball early on - but the second half was just not good enough."
Castleford: Platt, A. Fletcher, Shenton, McGoldrick, Dyer, Lupton, Brough, Sculthorpe, Henderson, Nutley, Manu, Ward, R. Fletcher.
Replacements: Bird, Viane, Fa'aoso, Davis.
Harlequins: McLinden, Stewart, Lucky Luisi, Smith, Bradley-Qalilawa, Sykes, Dorn, Mills, Randall, Heckenberg, Purdham, Hopkins, Paul.
Replacements: Williams, Haumono, Noone, Budworth.
Referee: P Bentham (RFL)