The young winger, a brother of Ulster and Ireland 'A' out-half Niall O'Connor, broke Armagh hearts as he took a whipped pass from replacement hooker Jason Mitchell to score in the corner in injury-time, levelling an end-to-end final at 17-17.
And the red and black ribbons of Armagh were loosened from the trophy when O'Connor, with admittedly 'nothing to lose' and extra-time looking likely, stepped up to plant a superb touchline conversion through the uprights and complete a magical cup run for the Bevan Lynch-coached side.
It was a disastrous finish for a determined Armagh outfit. Out-half Adam Gowing's fourth penalty goal of the afternoon had them 17-12 ahead and just before O'Connor touched down, lively winger Matthew Irwin, the scorer of Armagh's first try, had been stopped just short of the Derry whitewash following a pacy break.
All-Ireland champions, it sounds very sweet and match winner O'Connor, who has played for Ulster Ravens and Ulster Colleges this season, was proud as punch to win it for his club.
Speaking to IrishRugby.ie about that crucial kick, he said: "I just stuck to my routine. That's what I'm good at, usually I can kick my goals. I went through the routine, I had practiced a lot which helps!
"After scoring the try, I was out on my feet. The boys just came over and said, 'look, take your time, settle down, you have plenty of time.' I did, I had nothing to lose. I stuck to my routine, kicked it over and luckily enough I looked up and it was going through.
"I had missed a couple before, so I had nothing to lose and I just thought, 'go for it.'
"It was a good game to play in, it was physical, exciting, everything you want in a cup final. It was just a real dogged cup final, that's what we expected and that's what we got.
"We weren't really satisfied at half-time (leading 12-9), we thought we could have taken more chances and we let them back into the game.
"Adam Gowing kicked well. A lot of credit to Armagh for the game they put in."
O'Connor praised the Derry coaches for putting the structures in place for this young side to prosper not only in Ulster but now at a national level.
"We've a good coaching structure at the club. Bevan Lynch, Terry McMaster and Markie Nicholl brought a lot of us guys into the squad just first year out of school last year, gelled us together and it's went well for two seasons.
"We were unbeaten in Ulster last season and we've just sort of carried it on. We lost to Armagh earlier in the season so this was a big game for us.
"It's absolutely amazing to win a national final. We owe it to our coaches for the amount of effort they put in and we owe it to ourselves for the amount of effort we put in.
"There's boys having to take weekends off, get off work or get off early. But no complaints, they just go about their business. Every guy in that changing room thoroughly deserves it."
Derry's late hero also had a word for his older brother Niall and the advice he gave to him on the morning of the final.
"He sent me a message there this morning, he texts me before every game. He just sent me a message and said: 'Nothing fancy, just do the basics. It's a cup final, basic wins it.'
"It's just advice like that, it's priceless coming from his level of experience with Ulster and Ireland 'A'.
"Any questions, kicking through the week. He's my man to go to, so it's just great to have him there," he added.
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