Cairns had seen his side race into a 19-0 lead at Malleny Park after just 21 minutes and at that point would have had a four-try bonus point on his mind.
However, the game was turned on its head in the second half and from the moment Boroughmuir back-row Craig Keddie touched down for a try just after the break the visitors were back in things.
In the end Currie held on – just – for a 19-17 win, but had two players yellow carded in the second period and seemed to lose the composure and solidity they had in the first 40 minutes.
Cairns said: “I am obviously happy to get a win, but I am really disappointed that we only played for 30 minutes.
“We came out of the blocks flying and played some of the rugby that we know we are capable of and from 19-0 up we should have kicked on and really put the result out of sight.
“However, the opposite seemed to happen and the boys switched off. You simply cannot do that at this level and it nearly cost us.
“Fair play to Boroughmuir, they improved and caused us a few problems, but we gave away far too many penalties and the shape seemed to disappear from our team.
“We will have to improve to keep our top-four challenge going.”
In the end Boroughmuir picked up a losing bonus point, but they have now lost their past seven league matches and sit in eighth.
Their stand-in captain Cal Davies said: “Given the way we came out in the second half we could perhaps even have gone on to win it and that shows the character we have in the squad.
“Heads certainly have not gone down, but we need to get a victory soon to get us back on track and push us up the table.”
After stand-off James Semple had hit the post with a penalty, Currie captain Ross Weston’s try gave them the lead after five minutes.
Full-back Harvey Elms then added a beauty in the 14th minute and when impressive centre Robbie Nelson went over in the 21st minute it was 19-0.
At that stage there looked like being only one winner, but Muir’s second half was impressive.
Their tries came from two by Keddie and one from Callum Reid, but the home side just managed to claim the victory in the end after a dramatic finale.