Holders CIYMS are beaten by Leinster, while there are wins for Waringstown, Instonians, The Hills, Phoenix, Pembroke and Balbriggan. The YMCA v Merrion game was abandoned.
Holders CIYMS crashed out as they lost by 45 runs against 2009 winners Leinster. The Rathmines side posted 270 for 9 with half centuries for Monil Patel and Joey Carroll.
The CIYMS reply was in deep trouble at 124 for 7, but they showed their fighting qualities as they rallied. Skipper John Matchett scored 107 (14 fours, 2 sixes) as he and Mark Best - a former Ulster rugby player - added 74 for the 8th wicket.
However, they left themselves too much to do, eventually bowled out for 225, with Peter Francis taking three wickets, plus two apiece for Joey Carroll, Mark Tonge and Saqib Bahadhur.
Six times winners Waringstown progressed but were given a tough fight by Clontarf. Chasing 215, the Castle Avenue side were right in the mix at 170 for 5 in the 42nd over, but lost their last five wickets for 15 to be 185 all out - two wickets apiece for former Irish internationals Phil Eaglestone and Greg Thompson, as well as James Mitchell.
Morgan Topping continued his fine form as he was the glue that held a depleted home side together - his unbeaten 71 getting them to 214/8 - which their bowling unit resolutely defended.
Phoenix ran out five-wicket winners at North Down as they made light work chasing down 220. Jed Wiggins (78) and Stephen Black (33) laid the base, and Tyrone Kane clubbed five sixes in a rapid 41 to speed them to victory. Jacob Mulder (56) and Ryan Haire (44) were the main contributors to North Down's 220 for 7.
Mark Donegan hit 7 sixes and 7 fours in a rapid century to propel two-times winners The Hills to an emphatic 179-run win at Middle Road.
The Milverton side piled on 338 for 7, with 50s for Cormac McLoughlin-Gavin and Nicolaj Laegsgaard, plus runs too for Bhavesh Lakotia )44) and Tomas Rooney-Murphy (31).
Michael Rippon took three wickets and top-scored for the hosts with 79,but they were bowled out for 159 - six wickets for Sean McNicholl and two for captain Andy Kavanagh.
Instonians excellent season continued as they knocked out last season's beaten finalists Lisburn by six wickets at Shaws Bridge.
Shane Dadswell took five wickets as Lisburn could only manage 165 - Nigel Jones top scoring with 43. An opening stand of 95 between the prolific Robert McKinley (51) and Nikolai Smith (48) broke the back of the chase, and a fluent 43 from Cade Carmichael ensured a comfortable win with more than 12 overs to spare.
2019 winners Pembroke enjoyed their trip to the Mardyke as they recorded a whopping 249-run win over Cork County. JJ Garth top-scored with 156 from 132 balls (10 fours. 5 sixes) as he shared stands of 140 for the opening wicket with Diarmaid Tucker (67) and 152 in 20 overs for the second with Nick Stapleton (85).
A final total of 327 for 3 was certainly a daunting one, and thus it proved as the Munster side was shot out for 78 - three wickets for Gavin Hoey, and two apiece for Paul Lawson, Piyush Sharma and Fiachra Tucker.
Balbriggan beat Railway Union in the all-Leinster clash to keep alive their hopes of a first all-Ireland success. They showed their depth once again, as they overcame a shaky start to post 252. Matthew Pollard hit 7 fours and 3 sixes in an excellent 73, while there was also a half century for Chris De Freitas (51).
The hosts had a solid start to the chase with Ashil Prakash making 60, but three wickets for Dylan Lues and two for Andrew Darroch gave the momentum to Balbriggan which they maintained to close out a hard-fought 34-run win.
The game between YMCA and Merrion was abandoned after seven overs by the umpires who considered the pitch to be dangerous. The matter will now be considered by Cricket Ireland once they receive the official report. The most likely outcome will be a replay at Anglesea Road given the extenuating circumstances of YMCA's tenure at the ground.