Holders Waringstown, YMCA, and Instonians join Merrion in the semi-final draw after victories on Sunday.
It was a stroll in the sunshine for Waringstown who beat five times winners North County by 8 wickets after dismissing them for just 107 at Balrothery.
Cobus Pienaar took 3 for 31 with Phil Eaglestone and Gary Kidd each took 2 for 27 in a disciplined bowling display - Andrew Sheridan's 29 down the order getting County past the 100 mark.
James McCollum hit 10 fours and a six in an unbeaten 64 as they raced to the win in 18.5 overs.
Instonians had a 63 run win in Phoenix Park after Nikolai Smith's 94 took them to 290 for 9.
Irish internationals Andrew White (70) and James Shannon (45) were also among the runs in a fine batting performance.
Nicolas Pretorius 97 briefly threatened a close contest, but three wickets apiece from Nathan Smith and Stephen Bunting sealed the win.
Harry Tector's fine all-round performance kept alive YMCA's dreams of winning their first Irish Senior trophy as they overcame CIYMS by 46 runs at Claremont Road.
He hit 51 and took the crucial wickets of Justin Kemp and Johnny Thompson as CIYMS briefly threatened to chase down YMCA's 248 for 5.
Tom Fisher (66), Simi Singh (40) and Sam Murphy (32) were also among the runs in a solid batting effort.
Eight CIYMS players reached double figures in the run chase but none were able to deliver the major innings required to overhaul the total.
The draw for the semi-final will take place during the lunch interval of the Ireland versus Afghanistan final ODI at Stormont on Tuesday.