Melrose earned an opening- day victory at The Greenyards, scoring eight tries.
But Boroughmuir stormed back to gain a bonus point with four tries of their own.
Melrose dominated the first half after Jason Baggot found space to go over in only three minutes.
But, when Fraser Thomson was yellow-carded, the visitors made the extra man count and Thomas Gracie drove over the line. Chris Laidlaw converted.
George Taylor put Melrose back in front with a penalty, then Ross McCann went over, with Taylor supplying the conversion.
Melrose consolidated their lead with a third try from James Head and Taylor converted for a 22-7 half-time lead.
Boroughmuir’s hopes were swept aside as Melrose rattled in two tries in five minutes after the break.
Bruce Colvine got the first and Taylor converted, and from the restart, Baggot broke through for his second.
Jordon Edmunds scored and Laidlaw converted to lift the Muir’s spirits.
However, tries from Murdo McAndrew and Neil Irvine-Hess and a Taylor conversion put Melrose on easy street.
Andy Rose and Craig Keddie scored before McCann and Austin Lockington brought up 50 points.