Bosc kicked both conversions but Castleford drew level after 57 minutes with a Westerman penalty.
Catalans managed to open the scoring when Thomas Bosc found Dureau, who in turn fed Farrar.
Centre John Wilson extended Catalans' lead after the break, with Thomas Bosc adding the extras with the boot.
Thomas Bosc converted tries from Olivier Elima and Justin Murphy as the Dragons led 12-0 at the interval.
And victory was achieved without their half-back pairing of Adam Mogg, injured against Wigan, and the still sidelined Thomas Bosc.
The winger took Bosc's cut-out pass to touch down on 18 minutes and then wrong-footed Kevin Penny for his second.
Scrum-half Thomas Bosc's eight kicks sealed the win to move the Dragons to within five points of top side Leeds.
But after trading tries, Greenshields towered above full-back Matt Sing to take in Bosc's kick and score under the posts.
Bosc added the extras, becoming the first Catalans player to break the 300-point mark in the Super League in the process.
Bosc produced a wonderfully delayed pass to send Elima over, while Mogg created a stunning overlap that allowed Yeaman to benefit.
And two quick tries from Bosc and Jamel Fakir put the Dragons on top, despite a late Giants score from Darrell Griffin.
Bosc again made no mistake with the boot in front of just under 10, 000 spectators at the Stade Gilbert Brutus in Perpignan.
Greenshields ran over this third try of the game with 10 minutes remaining which Bosc converted to open up a sizeable advantage.
First, loose forward Mounis finished off a neat handling move and then Croker, Super League's oldest player, was first to Bosc's kick through.
But after the break, a brilliant running move involving Bosc, Clinton Greenshields and Justin Murphy gave McGuire the chance to score out wide.
BBC: SPORT | Rugby League | My Club | Catalans Dragons 30-22 Leeds
Thomas Bosc gave the visitors the early lead with two penalties before Jamahl Lolesi put the Giants ahead three minutes before the half-time interval.
Trailing 12-2 at half-time, Gregory Mounis, Jason Croker and Thomas Bosc scored tries after the break with Bosc adding three goals and a drop goal.
Dimitri Pelo opened the scoring after only two minutes with his sixth try of the season and Thomas Bosc kicked the first of five goals.
Bosc's clever hanging kick allowed Greenshields to touch down and then a teasing grubber from Bosc saw McGuire dive full length to ground the ball.
But the home side could have sewn up the victory had Bosc slotted over a regulation penalty 20m from Wigan's posts halfway through the second half.
Castleford, who had Ryan McGoldrick sin-binned for persistent offside, pressed for an equalising score but Bosc clinched victory for the French side with a late drop-goal.
The decisive score came 11 minutes from the end when Bosc forced his way over for the Dragons' third try, and he added his fourth goal.
Olivier Elima got on the end of Thomas Bosc's high ball to score for France before Josh Morris matched twin brother Brett with two late touchdowns.
Bosc then found Pelo unmarked on the left wing to create a fourth try and landed a third conversion to give his side a 20-point cushion.
Bosc's second goal made it 12-4 and England would have been even further behind at half-time had the stand-off been able to land a 50m penalty.
Bosc was the orchestrator of the Dragons' third try, lofting a high-ball for Wilson, who took full advantage of confusion in the Wigan defence to touch down.
The French side went behind to an early Chris Hicks penalty but led 22-2 at half-time thanks to tries from Murphy (2), Thomas Bosc and Dimitri Pelo.
Bosc made the Wolves pay with another try nine minutes before the break, re-gathering possession after Martin Gleeson had succeeded only in knocking the ball to ground.
But all French resistance crumbled when left wing Hall snapped up Bosc's pass near his own line and raced unopposed for his 34th try of the season.
Bosc again converted the extras but Richards, who kicked seven times in the match, kept his composure with the boot moments later to level the scores at 20-20.
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