It was the decisive score during an equally important spell, when the Cork school registered 1-4 without reply to gain a winning grip.
The teams were level six times in the opening 38 minutes and were tied at 0-8 apiece before Christians found another gear.
After the accurate Willie Barry pointed his fourth free to keep the Limerick school in the hunt, their opponents responded immediately with a super point on the run from the equally impressive Shane Barrett.
The Blarney marksman pointed a free a couple of minutes later to open up a two-point gap for the first time in a well-contested affair before the holders pounced for the all-important goal.
A long ball into the heart of the Doon defence was gathered by the alert Padraig Power, whose first instinct, just like his colleagues up front, was to run at opponents. That created the space and time to pick-out Cain close to the target and he duly tucked away his opportunity.
Two more Barrett points stretched the advantage to 1-12 to 0-8 with five minutes’ regulation time left, Doon having gone 20 minutes without a score. They did manage a 59th-minute goal from Bob Purcell, but even with three minutes’ injury-time, Doon couldn’t add to their tally.
Christians led by 0-6 to 0-5 at the break, the bulk of the scores coming from Barrett and Barry.
S Barrett (0-10, 7 frees); B Cain (1-0); D O’Hanlon and P Power (0-1 each).
W Barry (0-5, 4 frees); B Purcell (1-1), C O’Dwyer, C Berkery (0-1 each).
C Long (Glen Rovers); C Murphy (Sarsfields), S Green (Blackrock), captain, D Murphy (Sarsfields); E Doody (Blarney), C O’Donovan (Douglas), D O’Mahony (Sarsfields); D O’Hanlon (Blarney), D Quill (do); S Barrett (do), N Hartnett (Douglas), B Cain (Blackrock); J Scally (Bishopstown), P Power (Blarney), K Finn (Midleton).
K Coghlan (Courcey Rovers) for Quill 47.
E Doyle (Doon); P Barry (Cappawhite), D Fox (Annacarty), C Fitzgibbon (Cappamore); R Renehan (Cappawhite), B Murphy (do), captain, C Ryan (Doon); J Sheehan (Cappamore), D Hickey (Murroe-Boher); C Berkery (Doon), P Purcell (do), W Barry (Cappawhite); G Ryan (Cappamore), C Mooney (Annacarty), C O’Dwyer (Cappawhite).
D McCarthy (Cappawhite) for G Ryan 47.
W Barrett (Tipperary).