The Glebe Park outfit never really showed any ambition.
With Saints two up at half-time courtesy of two simple goals, the division's bottom club Brechin looked down and out.
So poor are they that the Saints keeper, Matt Glennon, stayed on the pitch at the break to warm up for the second half because he hadn't made a save.
Kevin Rutkiewicz slammed home the opener on 23 minutes after a well-rehearsed free-kick with Paul Sheerin saw the ball bounce to the Saints central defender eight yards from goal.
The second came from Kevin James doing what he does best, heading in virtually on the goal-line from a Darren Sheridan corner.
Saints' third was the best of the game, hit by Sheerin on 66 minutes. The boring Brechin boys had played the offside trap throughout the game, but a neat lofted through ball by Jason Scotland caught them napping. With the visitors standing static claiming offside, Sheerin stepped in to slot the ball home.
This well-deserved victory nicely sets up St Johnstone for their next home game in two weeks against league leaders St Mirren. Victory over St Mirren will take them to within four points of top spot.