Hore kicked six penalties while Cusiter scored a vital try as Borders recorded their third win in a row and their second shock win over their local rivals in the space of nine months.
In a scrappy and untidy game, Hore and Edinburgh’s Chris Paterson shared three penalties in the first eight minutes, Paterson’s efforts coming either side of Hore’s longer range effort .
Reivers did find some cohesion on the half hour after Semo Sititi made ground before handing the ball onto Garry Law, Simon Danielli and Wayne McEntee to set them up deep in Edinburgh territory.
However all the hard work came to naught as the Gunners turned over the ball.
Sititi then set up Danielli for a shot at the try line but he was barged into touch by scrum-half Mikey Blair just short of the line.
Reivers were finally rewarded for their efforts with another Hore penalty, and Hore kicked them into the lead in the dying seconds of the half with a 45 metre effort.
Hore slotted two more goals in quick fire order to open up a useful nine-point gap, before Cusiter beat Scotland Test rival Blair in a race for the ball to touchdown.
The rattled Gunners hit back with a late try through Ally Kellock but it was scant consolation.