It promises to be an enthralling final day at the Under 17 interprovincial series with three teams going into action with a genuine chance of clinching the trophy.
The Southern XI started the day in pole position but lost both their T20 matches allowing defending champions Leinster and hosts NCU to join them at the top of the table on six points.
Alex Stiles hit 8 fours and 4 sixes as he raced to 84 from 65 balls, adding 129 with Seamus Lynch (57) as Leinster made 167 for 4.
That was 36 too many for the Southern side, despite a rapid 38 from Seanan Jones (6 fours, 1 six).
Theo Dempsey, Scott Ruttle, Alex Neary and Cian Nulty each picked up two wickets.
In the afternoon match, they failed to chase down the NCU's 151 for 5.
Ben Askew got 27 and Jones 26 but they could only manage 123 all out, with Michael Glass taking three wickets, while Max Burton and Luke Allison got two apiece.
Oliver Metcalfe (48) and James Hunter (36) were the main run scorers for the Belfast side.
That completed a fine all-round day for the NCU, as they held their nerve to beat the NW in the morning match at Carrick.
Reece Malone (45) and Harry Warke (43) helped their side to 140 for 5.
The NW recovered from 38-4 to reach 101-4 with Tommy Orr (42) and Kyle Magee (30) to the fore.
The NCU bowling unit however closed out a 12-run win with two wickets apiece for Michael Glass, Max Burton, Luke Allison and James Hunter.
The NW however gained their first win of the competition in the afternoon game as they put a serious dent in Leinster's title ambitions.
Bready seamer Gregory McFaul took a hat-trick , and William Finlay two wickets, to reduce Leinster to 24 for 6, but they recovered to post 116, with Cian Nulty hitting 33.
JJ Garth (2-8) and Gavin Hoey (2-18) reduced the NW to 64 for 6, but Alistair Doherty (32*) and Kyle Magee (30*) got them over the line with a 53-run stand.
Friday's games see Leinster and the NCU facing off at Campbell College (11am), while the other match sees the Southern XI taking on the NW at Carrickfergus.
Leinster (4) beat Southern XI (0) by 36 runs. Campbell College, 5 July.
Leinster 167-4 (20.0 overs, A Stiles 84, S Jones 57, S Jones 2-31) Southern XI 131-8 (20.0 overs, S Jones 38, H Archer 29, T Dempsey 2-2, C Nulty 2-11, S Ruttle 2-25)
NCU (4) beat North West (0) by 12 runs. Middle Road, 5 July.
NCU 140-5 (20.0 overs, R Malone 45, H Warke 43, C Knight 2-13) North West 128 (19.3 overs, T Orr 42, K Magee 30, M Glass 2-8, J Hunter 2-18, M Burton 2-22)
NCU (4) beat Southern XI (0) by 28 runs. Campbell College, 5 July.
NCU 151-5 (20.0 overs, O Metcalfe 48, J Hunter 36) Southern XI 123 (19.0 overs, B Askew 27, S Jones 26, M Collins 25, M Glass 3-13, M Burton 2-9, L Allison 2-23)
North West (4) beat Leinster (0) by 4 wickets. Middle Road, 5 July.
Leinster 116-8 (20.0 overs, C Nulty 33, G McFaul 3-16, W Finlay 2-18) North West 117-6 (17.4 overs, A Doherty 32*, K Magee 30*, JJ Garth 2-8, G Hoey 2-18)