Castle's Alex Gleeson and Tramore's Robin Dawson are tied for tenth and just three shots off the lead after the opening round of the 13th South American Amateur Championship in Argentina.
And there was also a solid start for the Irish in the women's event with Lurgan's Annabel Wilson joint 11th, just four off the pace after a 72, as Liburn's Paula Grant posted a 76 to share 29th.
Gleeson and Dawson both made four birdies and two bogeys in two-under 70s at Martindale Country Club on the outskirts of Buenos Aires where Argentina's Alejandro Tosti and Scotland's Callum Fyfe carded five-under 67s in hot and humid conditions.
Despite the heat — the temperature reached 30C — they lead by a shot from Paraguay's Gustavo Silvero, American Scott Harvey, Mexico's Aaron Terrazas, Colombia's Pablo Andrés Torres and Argentina's Horacio Carbonetti.
In the women's event, Scotland's Shannon McWilliam and Colombia's Silvia Garces shot four-under 68s to lead by a stroke from defending champion Isabella Fierro from Mexico.
Wilson turned in one-under par on Martindale's back nine then got to three-under with four holes to play after birdies at the first and second before fading with bogeys at the sixth, seventh and ninth.
Grant was four-over after six holes and while she would make another four bogeys, she also notched four birdies to end the day tied for 29th in the 52-strong women's field.
1 ARG Alejandro TOSTI -5 67
1 SCO Calum FYFE -5 67
3 PAR Gustavo SILVERO -4 68
3 USA Scott HARVEY -4 68
3 MEX Aaron TERRAZAS -4 68
3 COL Pablo Andres TORRES -4 68
3 ARG Horacio CARBONETTI -4 68
8 CHI Agustin ERRAZURIZ -3 69
8 COL Camilo AGUADO -3 69
10 ARG Federico SHIN -2 70
10 NZL Charlie HILLIER -2 70
10 ECU Rafael MIRANDA -2 70
10 VEN Manuel TORRES -2 70
10 IRL Alex GLEESON -2 70
10 ARG Andres SCHONBAUM -2 70
10 IRL Robin DAWSON -2 70
1 SCO Shannon Stevie MCWILLIAM -4 68
1 COL Silvia M. GARCES -4 68
3 MEX Isabella FIERRO -3 69
4 PER Luisa Mariana MESONES -2 70
4 COL Maria C SERRANO -2 70
4 PER Daniela BALLESTEROS -2 70
4 URU Ines RAPETTI -2 70
4 MEX Ingrid GUTIERREZ NUNEZ -2 70
9 PAR Milagros CHAVES -1 71
9 ARG Macarena AGUILERA -1 71
T11 IRL Annabel WILSON Par 72
T29 IRL Paula GRANT +4 76
2006 Guayaquil (ECU). Paola Moreno (COL). Sebastián Saavedra (ARG)
2007 Lima (PER). Martina Gavier (ARG). Esteban Martínez (ARG)
2008 Santiago (CHI). María Yacaman (COL). Christian Espinoza (CHI)
2009 Sao Paulo (BRA). Paz Echeverría (CHI). Tomas Cocha (ARG)
2010 Bucaramanga (COL). Juliana Murcia (COL). Tomas Cocha (ARG)
2011 Bucaramanga (COL). Manuela Carbajo (ARG). Franco Romero (ARG)
2012 Cali (COL). Delfina Acosta (ARG). Jorge Fernandez (ARG)
2013 Bogotá (COL). Brooke Henderson (CAN). Callum Shinkwin (ING)
2014 Barranquilla (COL). Lucia Gutiérrez (PER). Paul Howard (ING)
2015 Lima (PER). Scott Harvey (USA). Sofía García (PAR)
2016 Lima (PER). Juan Álvarez (URU). Sofía García (PAR)
2017 Buenos Aires (ARG). Isabella Fierro (MEX). Paul Chaplet (COSTA RICA