Swatragh were keeping pace well with the holders in a terrific game and the teams were neck and neck entering the last 5 minutes.
Lavey had introduced McElroy just a minute or two earlier and she fired in three late goals to put Lavey through on a 7-9 to 4-9 scoreline.
It was a cruel blow for Swatragh who put in a tremendous effort – especially Una Mullan who fired home 3-2 of her own.
Lavey’s tactic of opening space in front of Mary O’Kane also paid dividends and she grabbed some great scores as well as opening space for others to get in on goal.
However the young impact sub changed a game that looked like heading for a replay and Lavey go through to a quarter-final meeting with Bellaghy next month.
Also through are Ballinderry who had a straight-forward 1-8 to 1-2 victory over Ballinascreen and their reward is a meeting with Premiership rookies Eoghan Rua.
Lavey : Teresa McElroy 3-0, Mary O’Kane 2-1, Helen O’Neill 1-2, Paula McCloy 1-1, Attracta McPeake 0-3, Adele Henry 0-1, Donna Magill 0-1.
Swatragh : Una Mullan 3-2, Grainne McNicholl 1-0, Janet McGuckin 0-2, Aideen Mullan 0-2, Claire Scullin 0-1, Aileen Tohill 0-1, Paula McAtamney 0-1.
There was some consolation for Swatragh’s Aideen Mullan as she won the Ulster Senior Poc Fada competition on Carntogher Mountain on Saturday.
The provincial U16 title was claimed by Ciara Campbell from the RuairÝ Ëg club in Cushendall who covered the course in 71 strikes.
Karen Kielt was in superb form as Kilrea rather easily defeated neighbours Ballerin in the Derry Senior championship.
An early injury to Ballerin’s county star Sinead Cassidy left them lacking leadership, but Sinead is now a big doubt ahead of the Ulster Senior final with Antrim this coming Sunday.
Liatroim Fontenoys have regained the Feis an Duin Senior Sevens title with a 5-14 to 1-1 victory over an under-strength Clonduff side. Kelly O’Higgins scored three of the goals and a number of points.
The Under 16 Feis final was much more closely contested with An Riocht edging out Portaferry by a point in extra time.
Feis na nGleann in Antrim is 15-a-side but Loughgiel still managed to pick up a treble of titles – Senior, Junior and under 16.
Portglenone fell in the senior decider, while they had a whopping 4-19 to 2-2 win over Ahoghill in the Junior grade and then beat Ballycastle 4-6 to 2-4 in the under 16 grade.
Mid Ulster League final tonight Wednesday :
Ardboe (Tyrone) 3-18 Middletown (Armagh) 0-2
Ulster Colleges’ Fr Davies’ Cup final
St Colm’s Draperstown 2-3 St Patrick’s Keady 3-8
Derry Premier championship :
Lavey 7-9 Swatragh 4-9
Ballinderry 1-8 Ballinscreen 1-2
Senior championship :
Ballerin 1-4 Kilrea 4-10.
Feis na nGleann camogie finals in Dunloy :
Under 16s : Loughgiel 4-6 Ballycastle 2-4
Junior : Loughgiel 4-19 Ahoghill 2-2
Senior : Loughgiel 2-10 Portglenone 1-9
Feis an Duin Sevens finals :
Senior : Liatroim Fontenoys 5-14 Clonduff 1-1
Under 16s : An Riocht 3-4 Portaferry 2-6 (aet)