Bishop travelled to Marldon to play for the right to face Buckfastleigh Rangers in the semi-final.
Without five of the squad that beat Harbertonford the week before, United gambled on the fitness of Dave Chadwick, who was recalled to the side to play centre half alongside cousin Jack.
With Barling and Jones making up the back line, Palmer, Hanks Cousins and Back lined up across midfield with Liddle and Shaw up front. Veteran Clark was between the posts.
Shaw and Liddle's running caused the home side lots of problems and, six minutes in, it was Shaw who latched on to a pass from Hanks to run through and calmly slot the ball past the advancing keeper.
Marldon pressed, but United soaked up the pressure and defended valiantly, looking to hit the home side with quick breaks.
A rash tackle saw Shaw brought down on the edge of the 18-yard box.
Matt Back took the free kick, bending it around the corner of the wall and inside the far post for a 2-0 lead.
As half-time drew near, Marldon forced a succession of corners. They finally broke through when Roach dived to head home.
Bishop started the second half on the front foot, Palmer and Barling combining well down the left and Jones and back again creating chances down the right.
On the hour mark Bishop forced a corner. Palmer swung the ball in and as Hanks went for it he was fouled. The referee pointed to the spot and Matt Back confidently found the net with a crisp drive into the bottom corner.
Shaw then beat four defenders only to place his shot wide of the post with Palmer, to his left, screaming for a pass.
Liddle was the victim of an over zealous challenge and was forced to go off. Williams took his place and within minutes found himself free, but the chance was wasted.
Marldon made some changes to try to get back in the game.
However, the visiting defence held strong and, at the final whistle, Bishop celebrated a hard fought victory against a team who are currently top of Division Five.
Player of the match was Scott Hanks.