The race for the title took another twist as Clontarf imploded at North County while Pembroke fought back to beat Phoenix by one run in a thriller.
Clontarf were skittled for just 66 on a damp Balrothery pitch - Fionn Hand (4-4), Terry Richardson (3-22) and Eddie Richardson (2-18) doing the damage.
Alex Cusack (3-16) struck early blows but Andrew Sheridan's 37 not out sealed the win.
Pembroke looked to be heading for defeat as Nicolaas Pretorius hit 89 from 97 balls (6 fours, 3 sixes) to lead Phoenix to 160 for 3 chasing 197.
However Pembroke knew that Phoenix had a soft underbelly and so it proved as Paul Lawson and Josh Little each took three wickets - Little bowling Brawders in the last over to seal the one run win.
Railway Union stay bottom as they could only manage 82 against YMCA - Simi Singh (4-18) and James Parkinson (3-14) doing the damage.
YMCA juggled their line-up and almost messed it up - losing six wickets before getting over the line.
Merrion - without John Anderson - posted 193 at The Hills, but it proved woefully inadequate as half centuries from Cormac McLoughlin-Gavin and Hamid Shah sealed the 8 wickets win.
Bottom slot could well now be decided on Tuesday when Merrion take on Railway in a crucial T20 replay. A win for Merrion would condemn Railway to automatic relegation.
In the second division Leinster stay top after a dramatic tie with Malahide, while Cork County stay in the promotion hunt after a comfortable win at North Kildare.
Phoenix 196 (49.3 overs, N Pretorius 89, P Lawson 3-45, J Little 3-47, D Murphy 2-41)
North County 69-4 (16.0 overs, A Sheridan 37*, A Cusack 3-16)
YMCA 85-6 (19.4 overs, S Ullah 3-13)
The Hills 194-2 (44.0 overs, C McLoughlin-Gavin 75*, Hamid Shah 70)