Two goals in the first half by David Gold and Darren Lavery set the seal on the match.
Formartine are currently second in the Highland League table, unbeaten in 11 games, and were not expected to be a pushover
They had the ball in the Berwick net after only three minutes, but referee Alan Newlands blew for a foul on keeper Michael Andrews.
Formartine applied the early pressure and Andrews twice raced from his box to clear long balls down the middle.
Craig Dargo fired over with a first time shot for Berwick and Ross Gray looked a threat down the right, but the slippery conditions, caused by heavy overnight rain, meant some players struggled to keep their feet.
Berwick also had the ball in the net after 28 minutes when Dean Hoskins had a shot from distance which keeper Andrew Shearer fumbled and Paul Currie netted from the rebound, but the flag was raised for offside.
Rangers broke the deadlock after 35 minutes when Lee Currie fed Gray on the right and his inch-perfect cross to the back post was met with a header from Gold.
Minutes later a Stephen Tulloch header was saved by Shearer at the foot of his right post whilst Dargo tested him from distance.
Berwick made it 2-0 after 42 minutes when striker Darren Lavery turned in a cross from Lee Currie on the left.
In the second half Gray made a break from half-way but his final shot, under pressure, was always going high.
Shearer then made a good double save from Lee and Paul Currie in quick succession as Berwick tried to turn the screw.
Lavery then broke but his shot was tipped over for a corner by Shearer.
Formartine started to run out of ideas and they were restricted to shots from distance as Rangers kept them at arms’ length.
A Lee Currie free kick dipped over the crossbar as Berwick went in search of a third.
And there was further heartache for the visitors when Stuart Smith was sent off after 86 minutes for a second bookable offence.
Late in the game Shearer made a good save to deny substitute Dean Horribine.
Berwick: Andrews, Notman, Young, Tulloch, Hoskins, Gray (Willis 76), P Currie, L.Currie, Gold (Horribine 84), Dargo, Lavery (Dalziel 80).
Formartine: Shearer, Monroe, Smith, McKeown, Hay, Clark (Duguid 57), Napier, McVittie (Bagshaw 68), Keith, Anderson, Madle (McKay 62).
Bookings: Monroe 37 foul; McVittie 39 foul; Anderson 45 foul; Smith 46 foul - sent off 86 foul); Napier 93 foul;
Referee: Alan Newlands.