For much of the tussle, Muir looked on course to pull off a dramatic win - but once Hawks had harnessed the elements, the outcome was not in question.
Hawks went ahead when home stand-off Toby O'Reilly was penalised for failing to release the ball in contact, allowing the visitors to set up a line-out in the danger zone after which Peter Dalton ploughed over from close range. Mike Adamson followed up with the conversion.
Muir responded to snatch the initiative - although they were fortunate not to have winger Ross Cooke red-carded for a vicious looking challenge on Iain Monaghan.
The revival began when Hawks were pressed into giving away a penalty, which led to winger Rory Couper diving over in the corner.
Boroughmuir snatched the lead with a try between the posts by Calum Cusiter, and O'Reilly added the easy kick.
Malcolm Clapperton was the beneficiary of a kind bounce following a steepler from O'Reilly and raced over to score. O'Reilly duly converted.
Hawks pinned their opponents back on their line after the restart - and Stuart Smith slid over in the corner.
Ally Maclay claimed the third Hawks try following a powerful burst from substitute Gavin Mories.
Then Ricky Munday eluded his markers to make sure of the bonus point, Monaghan thumping over the kick from the touchline.