The surprise of the third round was the defeat of Rainey by Regent at Circular Road to earn a home tie with RBAI.
It was a fantastic display by the underdogs against their seeded opponents especially as they were convincingly defeated by them early in the season.
Regent coach Eric Sinnamon praised his players’ effort.
“I knew that when we were at full strength we were perfectly capable of taking on most teams. It was a great 15 man performance that led to us turning round that earlier defeat,” he said.
“When called upon we had to defend for long periods but our morale was high and we weathered the storms.
“Peter Eakin at out-half controlled the game with centre Aaron Culbert strong in defence. I must mention the front row of Matty Kane, Jared Purvis and Blair Savage who were resilient while Philip Patton excelled at No 8.
“Everyone played their hearts out — especially the defence in that critical period up to half-time,” he added.
Down High's Chris Campbell paid tribute to Regent.
He said: “We have no complaints. They did their homework and knew how to play us and we didn't respond.
“We had numerous opportunities in the first half and they rallied in the second. We should have been out of sight,” he added.
“We were favourites to win but were beaten. It was a bad day at the office and our worst performance of the season but full credit to Regent and I wish them all the best in the next round.”
Regent have had more than their share of injuries and fielded their strongest squad for the first time when they eliminated Larne Grammar 42-0 in the last round.
Regent suffered an early set-back on Saturday when Rainey took a penalty quickly and Oisin Quinn crossed for an unconverted try on three minutes.
Aaron Murphy increased the advantage with a penalty after 20 minutes but nine minutes later Regent struck back.
Eakin, the North Down cricketer, went in at the left hand corner for an unconverted try but the remainder of the half belonged to Rainey who should have been further ahead than 8-5 at the half-way stage.
Regent's try came 12 minutes into the second half. The ball was passed along the three-quarters and winger Rhys Thompson touched down in the corner.
Rainey came back in the final minutes but Regent stood firm.