It was cruel luck on Tipperary, who had 1-4 from outstanding centre-forward Mairead Morrissey, but Waterford showed true grit to dig out the result.
Delahunty is one of the finest exponents of long-range dead balls in the ladies game and she delivered when the pressure was at its most intense to make it third time lucky for Waterford in Division 3 deciders, following defeats in 2014 and 2015.
After goal chances came and went at both ends early on, Morrissey crashed home at the Town End to tie the scores at 1-0 to 0-3.
The sides were level twice more approaching half-time before Katie Murray netted for Waterford with the final score of the first-half.
This handed the winners a 1-7 to 1-5 interval lead.
Tipperary’s Gillian O’Brien had another goal chance well saved early in the second-half by Katie Hannon.
At the other end, Waterford’s Aileen Wall was denied by Patricia Hickey in the 39th minute.
Waterford continued to hold the upper hand but Tipp refused to yield and were rewarded late on when Morrissey bagged a brace of points to level at 1-12 apiece.
However, it was Delahunty who nailed the final twist.
M Morrissey (1-4); A Moloney (0-3, 1 free); G O’Brien (0-2); L O’Shea, E Hanley & E Carroll (0-1 each)
K Murray (1-2); M Delahunty (0-4, 3 frees); S Ryan (0-3, 2 frees); A Wall (0-2); L Wall & M Ryan (0-1 each)
P Hickey; B Condon, S Lambert, S Delahunty; A O’Dwyer, J Grant, C Mullins; L O’Shea, S Carew; C Walsh, M Morrissey, E Myles; A Moloney, G O’Brien, E Hanley
E Carroll for Walsh (25), A McCarthy for Hanley (50), C O’Dwyer for Mullins (55), A O’Shea for Carroll (58)
K Hannon; M Wall, M McGrath, L Wall; E Murray, M Dunford, A Mullaney; L Ryan, K Murray; M Delahunty, R Tobin, C McGrath; A Wall, G Kenneally, S Ryan
L Devine for McGrath (23), M Ryan for Tobin (39), C Hurley for Devine (44), N Fennell for L Ryan (46), L McGregor for Mullaney (53)
J Murphy (Carlow).