Hawick have now lost seven games in a row and are adrift by nine points and at the bottom of the table.
Straight from the kick off Boroughmuir were in the faces of the visitors with No.8 Craig Keddie carrying the ball from halfway to the 22 before being dragged down.
Hawick kicked clear but Muir came charging straight back and openside Matt Walker ran in the first try. Stand off Greg Cannie converted.
Hawick reacted positively, and hooker Fraser Renwick looked to have touched down but was judged to have knocked on in the act of scoring and play was brought back for an offside penalty. Full-back Ali Weir kicked the three points.
Boroughmuir bust through midfield again, this time scrum half Johnny Adams carrying the ball with support and winger Grant McConnell went in for the score. Cannie converted.
Hawick reduced the deficit with a second Weir penalty but a third Muir try came quickly as flanker Dan Marek picked up at the rear of a ruck and went round the side to score.
The bonus point try came only minutes later as another wide sweeping move had the Hawick defence crambling but they could not stop Muir full-back Ciarion Whyte muscling his way overn.
Hawick were down but not out with half an hour played. They passed up a simple penalty to kick for the corner, winning the lineout and setting up a maul that rolled over the line for captain Bruce McNeil to score. Weir missed the conversion.
Try-scorer McNeil was yellow-carded on the restart and although Hawick survived a few assaults on their line the fifth try seemed inevitable and it duly laid on a plate for Cannie to cross and then convert his own try.
Fourteen-man Hawick made their presence known with a second try right on half time, lock Craig Hamilton claiming the points and Weir kicking the conversion.
McNeil came back on for the second 40 but Muir went down to 14 as captain Mathews was yellow-carded. It didn’t stop the procession of tries as Whyte ran in the sixth behind the posts and Cannie converted.
Winger Jordan Edmunds was next on the score sheet as Hawick’s willingness to attack left them exposed at the back. Centre Mike Brown was next to take advantage for an eighth try. Whyte then carved a path towards the line before putting Rory Scott in for a ninth try, converted by Cannie. Replacement scrum-half Jack Hamilton got the tenth.