Berwick built up a 12-point lead from the first leg of the KO Cup quarter-final clash when they beat the Edinburgh 51-39 at Shielfield on Wednesday.
The victory gives the Bandits the advantage going into the second leg at Armadale on Friday, but they know that will be a completely different meeting.
Edinburgh had previously only lost one of their opening 24 meetings of the season in all competitions, and they arrived at Shielfield in confident mood.
But they were undone by Berwick super-sub Matej Kus, who was the star of the show, top-scoring with a best-of-the-season 17 points, which included five race wins.
Berwick opened the meeting with two 5-1s and after thet they were never headed.
They produced eight of the first nine race winners, and with top Edinburgh man Craig Cook having an off night - he started off with three third places - the visitors struggled to get a foothold in the match.
The Monarchs finally got their act together in the latter stages, providing the last six race winners, Cook winning twice, but at the half-way stage of the tie it was the Borderers who had their noses in front.
Berwick: Kus 17, Doolan 9+1, Wethers 8+1, Vissing 7+1, Bellego 6+2, Carr 2+1, Jensen 2.
Edinburgh: Cook 9, Sedgeman 7, Masters 7, Fricke 7, Worrall 6+2, Fox 2+1, Sneddon 1.