In front of the BBC Scotland cameras, two goals in the first half were enough to see Rangers triumph over their fellow Lowland League opponents, setting up a tie with Stirling Albion.
Alex Harris fired them in front with less than two minutes on the clock, turning to score from inside the box.
The lead was doubled on 28 minutes when Rangers broke from their own half and a shot from Harris took a big deflection off a defender.
On 36 minutes the visitors pulled a goal back when Josh Cooper shrugged off his marker on the right side of the area to score his fifth goal of the season.
Gretna threatened briefly, but Harris was denied a second goal with a good save from Matty Connolly before the break.
In the second half, a Scott Mackenzie shot was touched onto the post by Connolly, as Berwick comfortably saw out the game to progress to the next round.
Berwick return to Lowland League action on Saturday (September 25) when they face Spartans (away).
In the East of Scotland League, Tweedmouth Rangers beat Edinburgh South 2-1 at home in the King Cup 1st round. Next Saturday they are home to Thornton Hibs in the Division 1, A Conference.
In the Border Amateur League, Tweedmouth Amateurs reached the semi-final of the Wright Cup with a 7-2 home win over Earlston Rhymers, their goals coming from Aaron Hope, Jack Sprot and Luke Leah, all with two, and Michael Antcliffe.
Berwick Colts and Highfields United were both without games. Spittal Rovers also found themselves without a game when their match against Eyemouth United Amateurs was postponed due to a shortage of referees.
Fixtures for the BAL this Saturday (September 25) are:
Wright Cup SF - Tweedmouth Ams v Gala Hotspur; C League - Berwick Colts v Gala Fairydean Rovers; Collie Cup SF - Eyemouth United Ams v Spittal Rovers.
In the Northern Alliance, North Sunderland won 6-2 at home against Newbiggin Central in Division 3 with two goals from Kevin Elliott and one each from Sam Aldred, Andrew Baiilie, Richard Stanwix and Ross Moore. On Saturday, NS are away to Walker Central.