Worcester: (12) 20
Tries: Quinnell
Pens: Brown 5
Harlequins (17) 27
Tries: Brown, Strettle, Keogh
Cons: Mehrtens 3
Pens: Mehrtens 2
Harlequins snatched an unlikely win with three opportunistic tries to leave Worcester at the bottom of the table.
Full-back Mike Brown and wingers Dave Strettle and Simon Keogh punished some defensive errors and recalled Andrew Mehrtens added 12 points from kicks.
James Brown kicked five penalties for Worcester but they suffered when injuries to two Harlequins props forced uncontested scrums in the second half.
It was 70 minutes before flanker Gavin Quinnell crashed over from a line-out.
"The only crumb of comfort is that the two games we've lost in the last five days are ones we could easily have won.
"The test is what happens over the next few weeks. As a team we can either fragment or we can stay together."
"One of the big criticisms over the last few months has been that we haven't been putting games to bed - this time we did that.
"Worcester have a strong scrummaging and mauling game but they didn't really know how to use that possession."
Worcester: Delport; Havili, Rasmussen, Lombard, Garvey; Brown, M Powell; Taumoepeau, Lutui, Horsman, Gillies, Sanderson (capt), Harding, Horstmann.
Replacements: Morris, Fortey, Murphy, Quinnell, R Powell, Drahm, Tucker.
Harlequins: Brown; Strettle, Deane, Abbott, Keogh; Mehrtens, Gomarsall; Jones, Fuga, Ross, Kohn, Evans, Vos, Volley (capt), Easter
Replacements: Richards, Nebbett, Spanghero, Hala'Ufia, So'oialo, Jarvis, Duffy.