That result - a fourth win in four matches - should be enough to make them champions for a third time in five years.
Calderdale sit out the last round of fixtures and Furness are the only team who can catch them after their 22-10 win over Leeds at the weekend. The Cumbrians need to win by a minimum of 29-3 against Fylde on August 23 to topple Calderdale from their perch.
A dominant display by the home side at Mytholmroyd BC paved the way for victory over reigning champions South Derbyshire. Calderdale had 10 of the 12 winners and a 235-178 scoreline more than offset a 234-200 defeat at Rolls Royce S and SC, Derby, where there were four visiting winners.
None of the current first division sides have played at Mytholmroyd BC and home officials had hoped the varying pace of the green would catch out Derbyshire. So it proved.
Adrian Brier's 21-8 success over Neil Gibson was the best result as Calderdale won three of the first four jacks in the home contest.
Bernard Megson struggled against a county bowler who gave him little room and Philip Chalkley lost the fifth match on the card but from then on it was plain sailing for Calderdale, who had a clean sweep from numbers six to 12.
David Stansfield had a fine 21-9 success which was matched by debutant David Warburton, who made the most of playing on his home green.
Richard Lawton bowled exceptionally well to win 21-12 after being called in to replace the ill Alan Bray.
Captain Mark McGorlick held his nerve to win 21-20 after striking off his opponent's touching wood at 20-20.
In the last four jacks, Paul Demetriades twice struck his opponent off at 20-20 to pinch the point.
Simon Leeming was left on the green alone and produced some superb corner bowling to win 21-16 after it had been 12 across.
At the extensive Rolls Royce complex, skipper Mark Regan stressed the need to battle for every chalk and the players did just that, several fighting hard to rescue an apparently lost cause. The most notable example was Justin Harris, who was all-but 13 down but won the next five ends to reach a commendable 18.
At the other end of the scale, number one jack Steve Wilkinson lost the first five ends but finished a 21-17 winner.
Pride of place in the first four went to Dale Holdsworth, who was paired against the home team captain who was playing on his own home green. Holdsworth led 19-8 and withstood a spirited comeback to win 21-14.
The second set of four jacks produced two more winners with Regan edging a high quality 33 end marathon by 21-19 and Tony Riley beating a reserve player, who turned out to be a Derbyshire county regular, by 21-16.
At this stage Calderdale trailed the home team by just nine chalks. The last four Calderdale players all lost but young bloods Justin Harris and Gareth Swaine both turned serious deficits into narrow defeats to ensure a victory over the two legs.


RESULTS (Calderdale names first) - at Mytholmroyd BC: B.Megson (Mytholmroyd WMC) 9 D.Allsop 21, C.Austin (Mytholmroyd BC) 21 M.Ford 16, A,Brier (Elland WMC) 21 N.Gibson 8. P.Holroyd (Hill Crest) 21 T.Glasby 11, P.Chalkley (Hill Crest) 16 W.Penny 21, R.Lawton (Akroydon Vics) 21 M.Grattan 12, M.McGorlick (Akroydon Vics) 21 D.Carter 20, G.Bradford (Greetland) 21 L.Davies 15, D.Stansfield (Akroydon Vics) 21 B.Ryder 9, P.Demetriades (Elland WMC) 21 T.Batchelda 20, D.Warburton (Mytholmroyd BC) 21 D.Parkin 9, S.Leeming (Elland WM) 21 D.Redfern 16.
At Rolls Royce, Derby: S.Wilkinson (Clayton Vics) 21 D.Taylor 17, R.Hobson (Hill Crest) 16 R.Treece 21, D.Holdsworth (Holmfield) 21 N.Jellyman 14, S.King (Asa Briggs) 19 R.Gill 21, R.Holmes (Elland WMC) 8 E.Furniss 21, P.Smyth (Hill Crest) 14 S.Gibson 21, M.Regan (Hill Crest) 21 D.Fitchett 19, T.Riley (Clayton Vics) 21 C.Jackson 16, J.Harris (Hill Crest) 18 D.Penny 21, G.Swaine (Luddenden Foot) 17 C.Pearson 21, P.Gill (Clayton Vics) 12 S.Gibson 21, B.Harrison (Clayton Vics) 12 B.Woodstock 21.

STANDINGS (matches played in brackets): Calderdale (4) 80, Furness (3) 52, South Derbyshire (3) 47, Leeds (3) 40, Fylde (3) 37.