CSNI ran out comfortable winners against Instonians while defending champions Waringstown got their competition back on track with a 43-run win against Armagh.
Shane Getkate's 32 was the only highlight of a disappointing Instonians total of exactly 100 at Stormont, with two wickets apiece for Ben Adair, Andre Malan, Aaron Wright, and Matthew Foster.
Andre Malan and James Kennedy went cheaply, but a third wicket stand of 56 between Mark Ellison and Marcus Topping saw CSNI win by 8 wickets with ten balls remaining.
Ellison struck 5 fours and a six in his 44 from 47 balls, while Topping stroked 4 boundaries in his unbeaten 35.
At The Lawn, Waringstown got their defence back on track with a 43-run win over Armagh.
A solid batting display saw the top four all make at least 30, with Lee Nelson top scoring with 40. James McCollum (35*), Adam Dennison (31) and James Hall (30) also among the runs.
Nelson then took 3 for 8 to stunt the Armagh reply, and it took a hard-hit 61 by Armagh professional Shadley van Schalkwyck from 46 balls (4 fours, 4 sixes) to get the Mall side up to 100.
CSNI lead the group with full points from their two matches, followed by Instonians and Waringstown with one win each.
T20 Group Results
CSNI (4) beat Instonians (0) by 8 wickets. Stormont, 16 May.
Instonians 100 (19.4 overs, S Getkate 32, B Adair 2-12, A Wright 2-22, A Malan 2-23)
CSNI 101-2 (18.2 overs, M Ellison 44*, M Topping 35*)
Waringstown (4) beat Armagh (0) by 43 runs. The Lawn, 16 May.
Waringstown 143-3 (20.0 overs, L Nelson 40, J McCollum 35, A Dennison 31, A Whitcroft 2-21)
Armagh 100-8 (20.0 overs, S van Schalkwyck 61, L Nelson 3-8, P Eaglestone 2-25)