Haig, who thumped 148 for Albion in the senior competition on Saturday, scored an undefeated 120 to steer his side to a seven-wicket win.
Chasing 225 for victory, Haig smashed seven sixes and nine fours. He found good support from Simon Butler (44) and Marcel McKenzie (22 not out).
Mat Harvie took two for 29 from five overs for Southland and Otago off-spin all-rounder Nathan McCullum conceded just 29 runs from his allotment of 10 overs.
Earlier, Shaun Fitzgibbon helped guide his side through to 224 for seven with a fine innings of 77, and James Wadworth scored 60.
Left-arm seamer Craig Smith took three for 42 from 10 overs and Jeremy Medlin bowled tightly, taking one for 40 from 10.
In the other match, Dunedin Metro had a narrow win over Otago Country. Batting first, Dunedin posted 263 for nine thanks largely to a nice innings by Ant Harris (83) at the top of the order. Otago wicketkeeper-batsman Derek de Boorder chipped in with 36 and Jordan Sheed 27.
Fraser took three for 37 from seven overs for Otago Country and Dion McCall two for 24 from six overs.
Country made a good beginning to its chase with opener Scott Simpson making 74. Craig Cumming, batting at No 4, continued his positive start to the summer with 67 and Warren McSkimming scored 37.
Seemingly on target for victory, Country self-destructed with unlikely hero Sean Eathorne taking five wickets in a five-over spell. Eathorne was more lucky than threatening but ripped through the middle order to help bowl Country out for 249.
Dion Lobb and Jamie Murley worked harder for their two wickets apiece and conspired to remove the top four.
