The 'tie of the round', a keenly contested affair at Downpatrick's Dunleath Park, saw Rangers race into the lead after a quarter-of-an-hour courtesy of a Courtney Hill finish.
It was a lead they held until the hour when Maeve McCaffrey levelled.
However Valley, superbly marshalled throughout by player-of-the-match Anna Cunningham, grabbed what proved to be the winner on 80 minutes when Elaine Orr converted from the spot.
Elsewhere, Bangor Ladies defeated Cumann Spoirt An Phobail at the Aurora thanks to an Allie Hamilton hat-trick, two from Shelley Crawford and a goal apiece from Rebecca McKenna and Jess Beers.
Carrick Rangers Ladies withstood a late Armagh City revival to win 4-3 at Taylor's Avenue with all four goals coming from the boot of the impressive Laura Aicken.
St. Matthew's Ladies also progressed following a two-goal away win over Downpatrick while PSNI Ladies and Dromore Amateur Ladies also kept clean sheets in their victories over Banbridge Town Ladies and Portadown Integrated Ladies respectively.
First Round results:-
Bangor Ladies 7-2 Cumann Spoirt An Phobail
Carrick Rangers Ladies 4-3 Armagh City Ladies
Celtic Ghirls Downpatrick 1-2 Valley Rangers Ladies
Downpatrick Ladies 0-2 St. Matthew's Ladies
Dromore Amateur Ladies 3-0 Portadown Integrated Ladies
PSNI Ladies 4-0 Banbridge Town Ladies
Celtic Ghirls Downpatrick and Valley Rangers
Player of the Match Anna Cunningham with Neil Morrow, IFA Women's Committee
Elaine Orr and Courtney Hill, Valley Rangers' goalscorers