CIYMS beat 2015 winners Brigade to claim their first Ulster Plate win in the final at Belmont.
David Allison's four-wicket haul meant the Beechgrove side were always on the back foot as they struggled batting first in bowler friendly conditions after the recent rain.
Stephen Scroggie top scored with 22 while Chris Dixon threatened briefly with 20, but they could only manage 107 with 8.1 overs unused.
The Belmont side attack all impressed with two wickets apiece for Henry Auchmuty, and the Robinsons - Chris and David.
Brigade skipper Mark Simpson did his best to haul his team back into the contest with a tidy spell conceding only 14 runs in his 8 overs and Waterstone had two wickets in two balls and finished with 3-32. However Alan Maitland's 33 and an unbeaten 22 from Barry Cooper sealed the six-wicket win with 27 balls to spare.
O'Neills Ulster Plate Final
At Belmont, CIYMS II beat Brigade II by 6 wickets.
Brigade II 107 (31.5 overs, S Scroggie 22, C Dixon 20, D Allison 4-31, C Robinson 2-11, H Auchmuty 2-15, D Robinson 2-19)
CIYMS II 110-4 (35.3 overs, A Maitland 33, B Cooper 22*, H Waterstone 3-32)