Bertram bagged four of his side’s nine tries, and there was one apiece by Scott McKean, DJ Innes, Andrew Chalmers, Ewan Miller and Scott McLeod, while Chalmers kicked the other points.
Accies, for whom Will Stephen booted three penalties, remained in touch at the break which they reached 20-9 in arrears but had no answer as Sonians stepped up the pace in the second period.
The win means that, with four games to go, Marcus Di Rollo’s men have now restored a five-point advantage over Marr at the head of the table, with both sides now having played the same number of matches.
Elsewhere, the points garnered from a 25-25 draw at home to Kelso have moved Musselburgh a step closer to guaranteeing their survival.
Meanwhile, two tries by Ross McCann and one each for Hugh Lindsay and Ali Greig yielded a bonus point for Stewart’s Melville who went down 36-25 at Jed-Forest on Friday night.
In Division Two, Lasswade secured a vital five points at home to Greenock Wanderers. Their 63-7 win has moved the Midlothian outfit out of the bottom two, although they have played four matches more than Whitecraigs, the side immediately below them.
Preston Lodge also managed to grind out a victory, seeing off Ardrossan Accies 14-12 at the Pennypit to remain in fifth spot.
Haddington’s hopes of featuring in the Division Three promotion race suffered a further dent when they went down 24-21 away to basement side Irvine. The East Lothian men now sit fourth, four points behind second-placed West of Scotland but having played two games more.
A depleted Livingston squad made the trip to Orkney and kept the score line blank for 30 minutes before the hosts took control to record a 45-5 win.
Meanwhile, RHC Cougars bowed out of the BT Cup at the hands of Cartha Queens Park after a last quarter fightback fell agonisingly short, losing 38-36.