Knock's Michael Sinclair won his first-round match on Monday
Leading qualifier Alex McCloy and Walker Cup player Jonathan Caldwell were among the losers in the opening round of matchplay at the Irish Close.
McCloy hit a sparking 65 on Sunday but he was edged out by Knock's Matthew Welsh by one hole at Belvoir Park.
Caldwell was beaten 1 up by Athlone's Ciaran O'Connor.
The Crowe brothers Darren and Simon and through to round two while other first-round winners included Connor Doran, Michael Sinclair and Gavin Reid.
Spa player Reid claimed a 2&1 win over Irish international Simon Ward while Doran defeated Moyola's Chris Selfridge by 3&2.
Darren Crowe defeated Belvoir Park's Chris Carvill 5&4 while his brother Stephen edged out Stacktown's Richard Bridges 3&2.
Carvill's brother David was beaten 4&3 by Royal Dublin's Niall Kearney.
Knock player Sinclair beat Dungannon's Johnny Mallon by one hole while Scrabo's Andrew McCormick defeated Westport's Cathal O'Malley at the 19th.
Sixteen-year-old Malone player Garth McGee beat Carrickfergus' Ross Oliver 4&3 while Belvoir Park's Harry Diamond defeated Fortwilliam's 3&2 in another all-Ulster battle.
Portstewart's Paul Cutler hammered Downpatrick's Dale Baker 6&5, Knock's James Patterson defeated County Sligo's Stephen Brady 3&2, Moyola Park's Paul O'Kane beat Limerick's Pat Murray 3&1 while Royal Belfast's Richard McDowell accounted for Athlone's Keelan McDonagh 2&1.
Ulster losers included Moyola's Luke Lennox, Donaghadee's Gareth Boyd, Shandon Park duo Alistair McKinley and Philip Purdy, Rosapenna's Ruaidhri Magee, Warrenpoint's Jim Carvill, Belvoir Park's Andrew Morris, Knock's Nicky Grant and Rathmore's Alan Dunbar.
Fancied Carvill lost 4&2 against County Sligo's Gary McDermott, while Boyd was beaten 3&2 by Irish international Paul O'Hanlon.
McKinley lost at the 19th against Fota Island's Thomas O'Flynn while Purdy was edged out by one hole by Headfort's Rory McNamara.
Holder Shane Lowery beat Ruaidhri Magee 4&3 while Dunbar lost 1 up against Cian Curley.
Host club hopeful Morris was beaten 5&3 by David Rawluk of the Island while Knock's Grant lost by hole against Mullingar's Des Morgan.