There were two hard-fought matches in the Women's league with YMCA beating Clontarf, while Leinster edged out Malahide in the other game.
Pembroke's match against The Hills was scrapped after the Milverton side withdrew their side from the top flight, and they will now play in Division Two only.
Hannah Ridgeway's run-a-ball 31 and 20 from Rebecca Stokell saw Leinster post 105 for 5 - two wickets apiece for Anna Kerrison and Isabel MacCormack.
Ridgeway shared a 5th wicket stand of 53 in 53 balls with Isabel Saeed-Maguire (13*) after they were in trouble at 49 for 4 just past the half-way mark.
It looked as if it wouldn't be enough especially with Leinster conceding too many extras, but twi wickets for Maria Kerrison and Jenny Sparrow ensured the nail-biting four-run win.
In the other match at Claremont Road, YM posted 150 for 4, with overseas player Kerrie Tomlinson (35) and skipper Gaby Lewis (31) getting the innings off to a fast start with an opening stand of 63 in 7.1 overs.
Jenny Gray (25) and Sarah Forbes (17*) also chipped in, with Isobel Joyce (1-13) doing her best to stem the tide of runs.
It was Joyce too who would star with the bat, but a lack of meaningful support meant she was ploughing a lonely furrow,
The former international hit 8 fours and cleared the ropes once as she top scored with 58 from 40 balls, but the other eight batters could only contribute 35 in total, as they posted 127 for 7.
YMCA rang the changes in the bowling, using eight in total, with Kate McEvoy the stand-out performer, taking 2 for 12 in her four overs spell.
LEINSTER SENIOR WOMEN LEAGUE
At Observatory Lane, Leinster beat Malahide by 4 runs
Leinster 105/5 (20 overs; H Ridgeway 31, R Stokell 20, M Kerrison 13; A Kerrison 2-10, I MacCormack 2-15)
Malahide 101/6 (20 overs; A Kerrison 17*; M Kerrison 2-13, J Sparrow 2-14)
At Claremont Road, YMCA beat Clontarf by 23 runs
YMCA 150/4 (20 overs; K Tomlinson 35, G Lewis 31, J Gray 25, S Forbes 17*; A Brennan 1-11, I Joyce 1-13)
Clontarf 127/7 (20 overs; I Joyce 58; K McEvoy 2-12, V Shukla 1-17)