RBAI advanced to the Danske Bank Schools' Cup final with a 10-6 win over Coleraine Academical Inst at the Kingspan Stadium yesterday afternoon.
The contest, which always looked likely to be decided by a single score, was won thanks to a second-half try from centre Callum McLaughlin despite the suggestion of a forward pass in the build-up.
All of Coleraine Inst's points came from the boot of Callum Smith and a late trip to the 22 could not spark a last-gasp comeback.
Richard Beggs, the defeated head coach, admitted that he suspected the crucial try should have perhaps been chalked off but refused to attribute any blame for the loss.
"I haven't seen a replay of it so I'll be doing an Arsene Wenger here," he joked.
"I don't want to criticise any official, it's an immensely hard thing to do in the heat of battle. It's fine margins.
"From where I was it looked close, I'd like to see it again."
Inst will now face the winner of tomorrow's second semi-final between Methody and Wallace High.
The Belfast school enjoyed much of the early possession, and moved the ball quickly along the backline, but the threat was too often curtailed by handling errors.
When the first points of the day did come, they went to Coleraine when a penalty from between the halfway and 10-metre lines was confidently knocked over by out-half Smith.
Undeterred, Inst continued in the same fashion and when Coleraine were penalised at the breakdown they took aim for the corner.
The lineout from just inside the 22 was untidy but Inst still maintained possession and, when Coleraine were pinged again, captain Lewis McNamara instructed TJ Morris to go for the posts.
There was a lengthy stoppage as Coleraine winger Niall Cameron received treatment for an injury but, after play resumed, the scrum-half restored parity.
The final 15 minutes of the half were a more even affair, with Inst still shading the possession but Coleraine's impressive back-row trio flooded the breakdown to stall the momentum.
When those loose forwards did stray towards illegality, the penalty was sent into the corner but an Inst knock-on from the subsequent line-out gave Coleraine the chance to clear, and the half finished 3-3.
After the turn, despite Daniel Soper and Richard Hedley sending on fresh legs in the front-row, Coleraine AI still had the edge in the scrum and, with conditions worsening, it seemed as if the battle between the packs would be the decisive factor.
However, 20 minutes into the half, Inst turned the ball over inside their own half and out-half Michael Lowry - starting in the 10 jersey as a fifth former - broke free.
Coleraine players seemed to feel that Lowry's offload to McLaughlin had drifted forward but there was no intervention from the referee.
The centre galloped home, despite a despairing dive from Thomas Lavery, and touched down underneath the posts to give Morris a straightforward conversion.
Another penalty from Smith - one of four Coleraine players who started last year's semi-final defeat to Sullivan Upper - reduced the deficit to four points but with five minutes left Inst thought they had sealed the contest.
Off the back of a solid scrum, Inst sent a long, probing kick towards the Coleraine line and, despite wing Joe Finnegan looking the favourite to win the footrace, he was thwarted by opposing full-back Matthew Smyth and a 22 drop out was awarded.
Buoyed, Coleraine upped the pressure and, after a break from Matthew Norris gained good ground, an Inst offside led to a penalty.
With the minutes ticking away, they went for the corner and Peter Wisener controlled the lineout deep inside the 22.
The forwards moved through the phases but, when the ball was spread out to the backs, Lavery was forced to check with the pass slightly behind him and he was bundled into touch.
It was to be the last meaningful attack of the game and moments later, just after the referee found a Coleraine forward with his hands in the ruck, Morris was gleefully booting the ball into touch to end the game and seal his side's place in the final.
Coleraine AI: M Smyth; N Cameron, M Norris, A Wisener, T Lavery; C Smith, B Campbell; D McAllister, D Greatorex, M O'Neill; J McCarroll, A Corbett; O McDowell, P Bonnar (captain), P Wiesner. Replacements: A McKee, A Moore, C Hamilton, J Bleakly, G Mawhinney, R Gillan, Z Hutchinson, C Skuce.
RBAI: A McGregor; J Finnegan, C McLaughlin, B McGavok, J Conlin; M Lowry, TJ Morris; J Chambers, Ryan McComiskey, J Dickson; G Bell, C Wallace; L McNamara (captain), E Harbinson, M Mairs. Replacements: C Reid, N Saulters, D Wallace, B Robinson, P Nicholas, M Young, P Dolaghan, M Keane.