Great Britain winger Ade Gardner took over as Super League's leading tryscorer as St Helens brought Catalans' eight-match unbeaten run to an end to leapfrog the French club into second place in the table.
Gardner's 14th and 15th tries of the season, which extended his scoring run in all matches to seven, finally ended the French resistance as Saints showed no mercy to their coach-in-waiting Mick Potter.
The Dragons' club record run began with a 24-10 victory over Saints in Perpignan in March but they never looked remotely capable of completing the double.
Potter, who will succeed St Helens boss Daniel Anderson at the end of the season, cannot fail to have been impressed by the home side's first-half display.
Their victory would have been more comfortable had Sean Long not missed four of his six kicks at goal.
Saints defended superbly to keep their line intact and only over-elaboration prevented them from building a bigger lead by half-time.
They scored the first of three first-half tries in the third minute when second rower Chris Flannery won the race to Long's grubber kick to the line.
The Dragons simply had no answer to the superb handling skills of stand-off Leon Pryce, who engineered a 21st-minute try for hooker Keiron Cunningham while prop James Graham took a short pass from substitute James Roby to crash over for their third try, to which Long added a second conversion.
The match was a repeat of last year's Challenge Cup final which Saints won 30-8 and they always looked destined to produce a similar result.
The French club suffered a blow when hooker Aaron Gorrell picked up a shoulder injury and they rarely threatened to breach an expertly-drilled home defence in a lacklustre first half.
They threatened to get back into the game when Thomas Bosc put his half-back partner Casey McGuire into a gap early in the second half and centre Adam Mogg was in support to score their first try.
But they continued to concede a string of penalties and full-back Clint Greenshields was sin-binned - for the second successive week - for interference at the play-the-ball and Saints made them pay for their indiscipline.
Gardner dropped Matt Gidley's pass with the line at his mercy and he was then brought back for a knock-on but he eventually broke the deadlock on 64 minutes when Cunningham and Long worked the ball wide.
He added a second eight minutes later following a break by Cunningham and Pryce jinked his way over for his side's sixth try, just before Greenshields scored a consolation effort for the outclassed visitors.
The only sour note for Saints came just before the end when second rower Lee Gilmour was helped off with a leg injury.