O'Leary combined with Jo Trendle in a massive opening stand of 198 to set up Wellington's score of 272 for two from its 50 overs yesterday.
Central Districts lost only one wicket in overtaking Otago's meagre tally of 64, and Canterbury fell well short of Auckland's 170 in the other game with Debbie Ramsay taking four for 15.
Short scoreboards:
Otago 64 (E Komp 2-15, C Forsyth 3-4) lost to Central Districts 65-1 (S McGlashan 32no).
Wellington 272-2 (A O'Leary 100, J Trendle 78) beat Northern Districts 127 (A Wilkins 50, J Stafford 23; A Cooper 2-20, A Corbin 2-21, P Gordon 2-27).
Auckland 170 (A Soma 55; C Moffat 3-36, H Tiffen 3-33, J Maley 3-9) beat Canterbury 116 (D Ramsay 4-15, O Johnson 2-21).