The visitors had looked impressive as they reached the break with an eight point advantage, but the home side stepped up a gear in the second half and used their superior forward power to dominate proceedings and post a deserved victory.
The visitors drew first blood in 21 minutes when Jason Baggott, who had missed with an earlier penalty attempt, sent an exquisite chip beyond two defenders and into the hands of winger Patrick Anderson, who touched down out wide.
Marc Morrison and Baggott exchanged penalties before the hosts claimed the lead when Karl Main capped a series of pick-and-drive attempts as he blasted his way over from close range and Morrison converted.
By half time, Knights had reclaimed the lead after Baggott landed a drop goal via a post, then added the conversion after Joe Jenkins had raced through a stretched Knights defence for his side’s second try to leave the Borderers 18-10 ahead.
Watsonians scored the first points of the second half when a penalty was despatched into touch and Cal Davies was on hand to apply the final touch after a powerful drive.
Baggott responded with a straightforward penalty, but the hosts had the momentum and they edged ahead in 50 minutes when another lineout drive ended with Steven Longwell blasting his way over from close range, leaving Morrison a conversion which he steered between the sticks for a single point advantage.
Morrison then booted a further three pointer and capped an impressive performance when he added the conversion after Sam Daly had forced his way over for the bonus point try late in the game.
The result means that third-placed Stirling County can cut the gap to the leading duo if they take a bonus point win from the trip to face Boroughmuir Bears at Meggetland tomorrow. Before then, Heriot’s will also have a similar objective when they travel to Millbrae to face Ayrshire Bulls.