The Scholars hung on against ten man Merstham to make it two away wins on the bounce.
Top scorer Josh Hutchinson gave Bar the best possible start netting the opening goal before many of the crowd were even in there seats putting the visitors ahead after just two minutes.
With Bar in rampant form both Brad Sach and Hutchinson had shots saved by the Moatsiders 'keeper Matte Pierson before Ben Ward Cochrane tested him with a fine free-kick which he touched over for a corner.
With 25 minutes gone the inevitable came as Hutchinson made it two, heading home from a near post flick on at a corner.
Just two minutes later Omar Folkes drove into the Potters Bar penalty box and was incensed not to get a penalty as he fell in the box. Amidst the protestation from the big striker he appeared to lash out at a Scholars defender leaving the referee but to show a red card .
With The Moatsiders down to ten men Bar looked to push home the advantage as Andy Lomas put in Hutchinson but his cross sat up a bit too high as Ward-Cochrane slid in to put it over the top.
With half -time approaching Merstham survived another Lomas shot whilst a Brad Sach shot was scrambled away to Thomas Gogo who could only fire over.
Two up with Merstham down the ten men The Bararmy must have enjoyed their half-time refreshment thinking the points were there for the taking.
But just three minutes into the second half any complacency from the fans turned to alarm as R'avan Constable misjudged a backpass to let in Shola Ayoola to tap into an empty net to put the home side back in it at 1-2 . Suddenly it was a very different game as the ten men apparently looked like twelve as Bar struggled to retain possession.
Ben Ward-Cochrane looked to have settled it just before the hour ; a Keagan Cole corner was headed back across goal from the back post and the lively striker restored the two goal cushion.
Merstham ,though, came back at a gallop forcing a corner on the left which centre back James Richmond headed narrowly wide. The home side continued to pressurise the Bar defence and pulled a second goal back on the 32nd minute as Edwin Mensah took advantage of some hesitant defending to head home and begin a very nervous last 15 minutes or so for the visitors before Scholars players and fans alike could breathe a huge sigh of relief.