Hawks scrum-half George Horne who was a constant threat around the fringes was a game changer for the Glasgow team.
Starting the game strongly, Hawks were 15-3 up with tries from Ross Thompson and Kyle Rowe, and penalty and conversion from Horne, with only an Andrew Chalmers penalty for the visitors.
Watsonians were brought back into the match just before the break with a converted try from Willie Thomson, making it 15-8 at the break.
Grant Stewart and George Horne put quick tries over for the home side in the second half before a rally from Watsonians saw Craig Borthwick, Sean Crombie and Mark Bertram bring it to within two points.
Glasgow Hawks flanker Callum Kerr put the game to bed with five minutes to go, bundling over and stealing a losing bonus point from Watsonians.
But both teams did get the four-try bonus point.