It was a day of high drama in the LCU as there were last gasp wins for Malahide and YMCA, while North County went top and Merrion won in Cork.
Clontarf lost their unbeaten league record as they went down by one wicket at YMCA in a game that went to the wire.
The Castle Avenue side racked up 246 for 4 with half centuries for skipper Eoghan Delany (77*), and Stephen Moreton (76) - Bobby Gamble (3-40) best with the ball.
Joe Morrissey then took five wickets as YM slumped to 120 for 6, but Simmi Singh hit 107 from 119 balls (15 fours, 1 six) got his team right back in the hunt.
Number 11 Padraic Flanagan proved the unlikely hero clubbing 21 not out off ten balls to seal the win - putting on 30 with JJ Cassidy (16*) for the last wicket.
There was, if anything, an even more dramatic win for Malahide at home to Pembroke.
Three were needed off the final ball with McAllister on 99 facing Ryan Hopkins - the former Irish international held his nerve to clinch the win and his own personal milestone.
David Rhoda scored an unbeaten 106 from 109 balls (10 fours, 2 sixes) as Merrion avenged their cup exit last week in Cork.
Merrion ran up 304 for 7, with Robin Smith (61) continuing his rich vein of form.
Morne Bauer hit 44 as Cork finished 103 runs adrift - Rhoda taking 3 for 45 and Tom Stanton also claiming three wickets.
North County assumed leadership of the table thanks to Nathan Rooney's 95 not out, and Eddie Richardson's 65.
County's 255 for 6 proved 120 too many for Railway Union - Adrian Murphy top scoring with 37.
In the second division, Nic Pretorius hit a century and Manu Kumar 70 as The Hills crushed Balbriggan.
Chasing 280, Balbriggan mustered just 98 - Kumar taking 5 for 23.
Terenure stay top of the pile thanks to a hard fought four wicket win over YM's second string.
34 apiece from Daan van Zyl and Diarmuid Lynch saw them chase down their modest 153 run target.