Three goals from Neil McManus gave Antrim the edge in a highly competitive battle at McKenna Park.
This victory puts Antrim within striking distance of a final place -- a win in their last game away to Limerick would send them into the final.
In a strongly contested game, three players were somewhat unlucky to be red-carded, with Antrim's Eddie McCloskey now ruled out of next week's clash. Down finished with 13 after Eoin Clarke and Fintan Conway saw red.
Antrim opened strongly with a point from McManus after four minutes and then he set up Karl Stewart for a goal.
Paul Braniff opened the Down account with a pointed free after seven minutes, but Antrim's reply was two goals from McManus as they led 3-4 to 0-5 at half-time.
Down played their best hurling in the third quarter, scoring four points, but again, Antrim struck back with two goals and a point in a two-minute spell with Stewart and McManus (from a penalty) finding the Down net.
Man of the Match: Neil McManus (Antrim)
Scorers -- Antrim: N McManus 3-5 (1-0 pen, 4f), K Stewart 2-1, S McCrory 0-2. Down: P Braniff 1-6 (4f), S Johnson, S Clarke, C O'Prey 0-2 each, S Nicholson, J Coyle 0-1 each.
Antrim -- C, O'Connell 7; A Graffin 7, K McGourty 7, K Molloy 7; N McAule 6, M Herro 7, J McCouaig 7; S McCrory 8, S McNaughton 7; P Shiels 6, K Stewart 8, E McCloskey 6; C McGuinness 6, N McManus 9, B McFall 6. Subs: K McKeegan 7 for C McGuinness (h-t); J Black 6 for S McNaughton (45); C McFall 6 for P Shiels (45).
Down -- K Keating 7; M Hughes 7, F Conway 6, S Ennis 7; C O'Prey 7, C Woods 8, M Ennis 8; A Savage 7, E Clarke 7; G Johnson 7, S Clarke 7, B Ennis 7; A O'Prey 6, P Braniff 8, J Coyle 6. Subs: C Mageean 7 for B Ennis (48); S Nicholson 7 for A O'Prey (48); D Hughes for S Clarke (66).
Ref -- J McGrath (Westmeath).