The Ballymena team had received a late recall to the tournament as Portadown were unable to further participate due to injury problems.
Rainey took a 3-0 lead when Scott McLean converted a penalty opportunity with just three minutes on the clock.
Ten minutes later Niall Keenan made good use of the ball and combined with Dylan Wilkinson to send the industrious Aidan McSwiggan under the posts for a try. McLean added the extras to increase the lead to 10-0.
Just after the mid-point of the first half a free flowing handling attack ended with Declan McCusker touching down to increase the Rainey lead.
The Ballymena team, despite losing their hard-working hooker, Dylan Hacine-Bacha to injury, never lost heart. Players such as Aaron Heaney, Ty Mackness and Ben McIlroy all asked questions of the Rainey defence but found no way through.
Just before the interval it was, once again, a combination of quality possession from a Rainey lineout and the effective use of the possession, that saw Islas finish with a try. McLean’s extras gave his side a 22-0 advantage at the break.
Two quick converted tries by McLean and Niall Keenan brought the score to 36-0 and effectively ended the Ballymena challenge. The Braidmen also lost a player to the sin bin and Rainey capitalised with a try by Michael McElhone from a well-organised driven maul. McLean was successful with his third touchline conversion.
Michael Gordon then collected a loose ball and ran clear for another try soon after, which McLean converted to bring his team’s tally to 50 points.
After the game the Nutty Krust Man of the Match Award was presented to Rainey winger, Odhran Islas, by Bobby Stewart, IRFU (Ulster Branch) Senior Vice-President.
The second semi-final of the 2015 Nutty Krust Tournament will take place on Wednesday night when Omagh take on Dromore (Chambers Park, 7.45pm).
The winners of that game will face Rainey in the final at the same venue on Wednesday 29th April.