Portora Royal were 12 points in arrears and fought back for a six points lead before a late Dalriada rally deprived them of a Northern Bank Schools' Cup third round place against Regent House, the Fermanagh school going down 20-16 in their weekend replay at Ballymoney.
It was always going to be a close contest after the teams played a 10-10 draw at Enniskillen last Saturday. Neither side dominated with the result uncertain right to the end.
Certainly Portora were the better team when they scored 15 points without reply but then appeared to ease off in the final quarter and allow their opponents back into the tie.
Dalriada played into the strong wind in the first period and took a 12-point advantage after a kick through by Johnny Allen allowed Jack Magee to score and John Laughlin to convert. Allen added the second in the corner before Patrick McCleery kicked a Portora penalty just on the interval.
The half-time talk did wonders for the visitors as they came out showing more determination and a line break by Johnny Magwood after five minutes led to a James Ferguson try under the posts to give McCleery the easy conversion. He then kicked a penalty before forward pressure resulted in Alex McCurry going in for a second try.
Portora were in control at this stage but Dalriada came back with a Laughlin penalty to reduce the deficit to three points and five minutes from the end ran in an excellent try, second row forward Tim Woods crashing over to put them through.
The only surprise in the Northern Bank Medallion Shield third round was the 14-5 defeat of Rainey Endowed at Portora who are always difficult to overcome on their own territory and were much superior on the day.
It was a double celebration for Dalriada as their Medallion side triumphed 13-12 in a closely contested tie at Dungannon Royal.
The fourth round draw will include the top eight seeds: RBAI, Campbell College, Sullivan Upper, Coleraine AI, Belfast Royal Academy, Methodist College, Wallace High and Ballymena Academy.
Other results: Limavady Grammar 3 Armagh Royal 8, Regent House 22 Foyle and Londonderry College. 5, Banbridge Academy. 7. Ballyclare High. 12, Down High 20 Carrick Grammar 15. Still to be contested: Belfast High v Friends' and. Dromore High v Portadown College.