Tries from Diack and Darren Cave opened up an eight-point half-time lead for the Ravenhill outfit who appeared to be coasting to a third successive victory.
But two Berquist penalties after the interval closed the gap to two and Diack admitted it had been a little too close for comfort despite climbing to third in the table.
"It's nice to get a try but all you want is for the team to play well," the No.8 told The Belfast Telegraph.
"I think in the last couple of games we've luckily come away with wins.
"We are disappointed in the way we played and in our discipline. Our set-piece wasn't what it was so the win was a relief.
"I think we let them in at our set-piece in the scrum in the first half and in the first one they got a penalty and that really got their tails up.
"They had a lot of firepower in their forwards and their backs and you just can't allow that to happen, but we did."
And Diack admitted that it would be back to the drawing board ahead of Friday's game against Newport.
"We've got to now focus on the Dragons. They've got a good team and it's going to be a hell of a confrontation. We're just looking forward to being back at Ravenhill," he added.
"These last couple of weeks have been stop-start and I think we're now looking forward to getting a bit of momentum from playing again.
"That's the best way to rectify things - to just get back on the pitch as quickly as possible and try and fix it."
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