Laura Delany's brilliant hundred helped Leinster to an emphatic 111-run win over title rivals Merrion as they leapfrogged the Anglesea Road side at the summit.
The Irish skipper hit 8 fours and a six as she raced to 103 from just 82 balls as Leinster posted 278 for 6.
Rebecca Stokell's hard-hit 59 got the innings off to a flying start from which Leinster never looked back.
Delany shared a third wicket stand of 107 with Isabelle Fitzgibbon, who made 41.
Sophie MacMahon (23) and Ellen Ridgeway (20) also chipped in to the impressive batting display.
Merrion were never in the hunt, with Sadbh Breslin top scoring with 34, while Cecelia Joyce hit 29 before being dismissed by Delany.
Merrion had gone into the game on top after winning a T20 game against Malahide at 9am on Sunday morning.
Mary Waldron made 51 in Malahide's total of 107 for 8, but an unbeaten 43 from Isobel Joyce, coupled with 24 from Leah Paul and 20 from skipper Rachel Delaney ensured the seven wicket win with three overs to spare.
Leinster now face Pembroke on Wednesday and Clontarf on Thursday, knowing wins in both games would secure the league title.
Clontarf's Kerry Tomlinson was another centurion, scoring an unbeaten 144 to pass the 1000 run landmark for the season as they beat The Hills.
Tomlinson hit 17 fours and 2 sixes in her 144 from 136 deliveries, sharing an opening stand of 117 with Una Raymond-Hoey (57), and 132 for the second with Tess Maritz (30) as they chased down their 269 target.
The Hills would have been happy at the half-way stage with their total of 268 for 9 - Alana Ryan (57), Miranda Andrews (46), and Amy Benson (36) the main contributors.
Keeva Vickers (4-37) was best with the ball for Clontarf.
The final match was a one-sided affair as Pembroke thumped YMCA.
Three wickets for Louise McCarthy (3-31), plus two apiece for Orla Prendergast and the Little sisters saw YM make just 107 - Emma McEvoy (28*) and Lucy O'Reilly (20) the only players to get starts.
It took just 10.1 overs for Pembroke to pass the modest target, with Orla Prendergast hitting 9 boundaries in her unbeaten 54 from 33 balls, while LuLu Little hit 7 fours in her quickfire 38.