Merrion ran out comfortable winners in both their contests, with skipper Rachel Delany and Leah Paul to the fore.
Both scored half centuries as they beat Malahide comfortably, with Delany also taking four wickets.
Paul also hit 50 in the T20 game against Clontarf, hitting four boundaries in an opening stand of 69 with Naomi Matthews (31).
Delaney chipped in with 22 as Merrion posted 148 for 3, with Isobel Joyce taking 2 for 17 against her former team-mates.
Joyce also top scored with 37 from just 19 balls (6 fours) but the Castle Avenue side struggled to 88 all out.
Matthews - named in the Irish squad to face West Indies later this month - took 3 for 22, while there were four run outs as well.
Closest game of the day was at Observatory Lane, where YMCA held their nerve to edge out Leinster.
Chasing 119, Leinster looked favourites at 59-0, and also needing seven to win in the final over.
However, they fell two runs short courtesy of a brilliant boundary catch from the final ball.
It's been a good few days for Mary Waldron as the Irish keeper became part of history as she was named one of six contracted women players.
She hit her second half century of the season as Pembroke beat Clontarf by seven wickets.
Waldron added 63 with fellow contractee Kim Garth (43), while the third Pembroke player awarded one, Shauna Kavanagh made 20.
Earlier Clontarf's total of 181 saw Isobel Joyce top score with 38 - Mullins claiming 3 for 19, and two wickets apiece for Anna Beale and Kim Garth.