The hosts ran in six tries to move two points clear of fourth-placed Leeds, who are on the same point as Catalans after a 46-12 demolition of Salford.
Tony Puletua, Mark Flanagan (two), Paul Wellens (two) and Anthony Laffranchi touched down as the Saints blew away their opponents.
London remain at second bottom of the table, level on points with Widnes.
In the night's other game, Leeds kept alive their hopes of a qualifying play-off place with an eight-try mauling of Salford.
Ben Jones-Bishop, Ryan Hall, Kevin Sinfield, Rob Burrow, Kallum Watkins (two), Weller Hauraki and Jamie Jones-Buchanan all crossed the line for Leeds while Salford could only muster two late efforts by Luke Patten.
Victory for Leeds saw them go above Catalans, who have a game in hand against Castleford on Sunday.