The Hartreemill hammering was Biggar’s sixth victory from seven Tennent’s National Division 1 outings this season and puts them two points ahead of Heriot’s at the summit with Melrose dropping to third place.
Yet Biggar suffered an early blow when Ross Bradford picked up a hamstring injury after his first run in the second minute and he was replaced by Mark Bertram.
Melrose’s Thomas Brown was shown a yellow after referee Sam O’Neill adjuged that the lock had illegally collapsed a Biggar driving maul.
Biggar took advantage of the extra man to score a pushover try credited to No8 Ross Jackson.
Andrew Jardine who, having been with Melrose for a year and who was particularly keen to put one over on his old team-mates, was wide with this conversion and the next one after Mulligan crashed over on the 10-minute mark.
And it was 17-0 when Jardine collected a Melrose pass and went down under the posts before kicking the conversion himself.
Winger Rowan Stewart then ran in untouched for the fourth try which Jardine converted for 24-0.
Melrose reduced the leeway before half-time when Douglas Crawford scored a try before kicking the conversion.
Biggar’s Rory Hutton was yellow carded early in the second half but Melrose failed to score while he was off.
A Borthwick try converted by Jardine, swiftly followed by a Rowan Stewart score, made it 36-7 for the hosts.
Ewan Stewart then touched down following a Biggar scrum, with Conor Lavery adding gthe conversion for 43-7.
Robbie Orr notched two further tries for Biggar who then had Peacock yellow carded for foul play at a ruck.
Lavery converted one of Orr’s double, before Connor Spence scored a late try for the visitors.
Biggar have no competitive fixture this Saturday.