CIYMS did what they had to do against CSNI and opened the gap to eight points between themselves and Waringstown, their only possible rivals for the title.
With only four matches to play for each of the contenders it will take a massive decline in the fortunes of CI if they are to surrender their position at the top.
Waringstown are winning all before them at the moment but their defeat to CI last week was crucial and they will also look back on a season where they lost to Carrickfergus both home and away.
CIYMS had a bit of a wobble in their chase of CSNI's 195 and it was Matt McGillivray (64*) and Jacob Mulder (38) who put on 94 for the 6th wicket to pull CI out of a hole at 82/5.
CSNI still missing Graeme McCarter and for whom Ellison and Malan failed to fire were helped to their 195 by another steadying innings from Arnie Wright with 44, Matt McGillivray taking 3-35.
Not the dominant performance from the league leaders that they would have hoped for but points in the bag at this stage of the season was the important thing.
Instonians got back to winning ways after back to back defeats with an emphatic performance against Carrickfergus.
There were fifties for Shane Getkate and Robert McKinley as the Old Boys totalled 282/6 with five of those wickets falling to Matty McCord for only 36 runs.
The Carrick reply never threatened with Michael Gilmour's top of the order 50 and Dan Poulton's 49 when the cause was lost the only significant scores.
For Instonians it was three wickets each for Andrew White and Ben Rose and two for Jordan Magee.
James Lambert who impressed in the NCU U16 festival earlier in the week only took one wicket but it was a significant notch on his belt as he claimed the wicket of Carrick professional Pat Botha.
The Friday night attempted to play a Match 2 between Muckamore and North Down fell foul of the weather and is now void.
So with Waringstown off claiming the All-Ireland T20 crown only two fixtures were played this Saturday.
Today (Sunday) CSNI are at home to Waringstown - CSNI are losing the services of Andre Malan who travels home today and will be hoping that the Waringstown celebrations last night will take the edge of their performance but I wouldn't be counting on that.
PREMIER LEAGUE RESULTS:
CSNI lost to CIYMS by 4 wickets. Stormont, 18 August.
CSNI 195-6 (50.0 overs, A Wright 44, C Goodall 29, M McGillivray 3-35, J Cameron-Dow 2-33)
CIYMS 199-6 (45.2 overs, M McGillivray 64*, J Mulder 38, C Dougherty 34, A Malan 4-44)
Instonians beat Carrickfergus by 91 runs. Shaw's Bridge, 18 August.
Instonians 282-6 (50.0 overs, S Getgate 76, R McKinley 67, A White 37, M McCord 5-36)
Carrickfergus 191 (42.5 overs, M Gilmour 50, D Poulton 49, A White 3- 27, B Rose 3-30, J Magee 2-32)
Muckamore v North Down - no result - now void. Moylena, 17 August.