Image | www.quins.co.uk
Used with permission
It was the London club's second win in the region in 10 days, following their challenge cup victory of Pia last Saturday.
Jon Wells handed the visitors an early lead before Thomas Bosc converted his own try to put the home side 6-4 up early on. But tries from Chad Randall, Danny Orr and Mark McLinden, together with four two-pointers from Henry Paul, saw Quins rack up a 24-6 advantage at the break.
Dmitri Pelo's try 6 minutes in to the second half gave Catalans hope of a comeback, but the game was as good as finished when Julien Rinaldi scored in his first outing against his former club on 49 minutes, stretching Quins' advantage to 30-10.
A Paul penalty made it 32-10 before Adel Fellous grabbed a consolation for the Dragons, converted by Bosc.
But it was Quins who had the last word, captain McLinden crossing for his second try, again goaled by Paul, to seal a 38-16 win, Quins' fourth of the season.
Harlequins coach Brian McDermott said: "We dominated the first half but they came out firing in the second period. They upped the ante and we had to match it. It was a massive defensive effort.
"Full credit to the players for the way they have approached this period. It is certainly paying off.
"But we must back it up against Wakefield on Saturday. It's no good us coming this far without another big performance."