Worcester (9) 15
Penalties: Goode 4 Drop Goals: Goode
Harlequins (3) 17
Tries: Smith, penalty try
Conversions: Evans 2 Penalties: Evans
Harlequins kept up their winning start to the season as they stole victory with two tries in the final 20 minutes.
Home stand-off Andy Goode kicked four penalties and a drop goal at Sixways to put Worcester 15-3 up on the hour.
But Sam Smith's try, which was improved by stand-off Nick Evans, brought 100 per cent Quins back to within a score.
And, after late pressure in which home flanker Jake Abbott was sin-binned, Quins won it seven minutes from time with a penalty try, converted by Evans.
But victory came at a cost for the visitors when star wing Ugo Monye limped off with an ankle injury on the half hour.
Worcester took an early lead when Goode kicked a fourth minute 25-metre penalty after Marcel Garvey's strong run had put the visitors on the back foot.
But referee Chris White awarded a flurry of penalties for various minor infringements and, after 17 minutes of disjointed play, Evans tied up the scores when Worcester were penalised for dragging down a maul.
Goode soon put Worcester back in front before slotting another monumental effort from five metres inside his own half, when the Warriors produced a fierce scrummage drive which sent the Quins pack backwards for almost 15 metres.
After enjoying a deserved interval lead, Worcester built up early pressure in the second half thanks to a huge clearance kick from Goode. And, when Quins gave away yet another penalty, Goode again made no mistake.
We need to have a serious think about who's making the errors
Worcester coach Richard Hill
Worcester went close to scoring the first try of the game when Neil Best charged down Karl Dickson's clearance kick, only for the subsequent drive to come up narrowly short.
But the Warriors were not to be denied a score, Goode dropping a goal with 25 minutes to go, which appeared to go between the sticks via a helping Quins hand.
The loss of influential skipper Kai Horstmann with a leg injury did not help Worcester's cause and, against the run of play on the hour, Evans produced an exquisite pass to send Smith on a 30-metre run to the line.
Evans converted to narrow the gap to five points and a revitalised Quins built up sustained pressure.
Time after time, they drove for the try-line but the home defence held firm until Worcester conceded penalties at a succession of five-metre scrums and, with seven minutes left, Abbot was sent to the sin bin.
That cost Worcester dearly, as from the next scrum, Quins were awarded a penalty try and Evans converted to complete the turnaround.
Warriors coach Richard Hill told BBC Hereford & Worcester:
"At 15-3 down they had no right to dig themselves out of that, but we made some poor decisions at bad times.
"We conceded a soft try from first phase, which should never have happened.
"We made eight unforced errors in the first 17 minutes and we need to have a serious think about who's making those errors."
Worcester: Claassens; Garvey, Grove, Rasmussen, Benjamin; Goode, Perry; Mullan, Fortey, Taumoepeau; Percival, Chris Jones; Best, Abbott, Horstmann.
Replacements: Shervington for Fortey (49), Douglas for Taumoepeau (55), Kvesic for Horstmann (57), Short for Garvey (59), Ceri Jones for Mullan (65), Gillies for Chris Jones (65), Frost for Perry (73)
Not used: Carlisle.
Sin bin: Abbott (73).
Harlequins: Brown; Smith, Lowe, Turner-Hall, Monye; Evans, Dickson; Lambert, Gray, Fairbrother; Kohn, Robson; Robshaw, Wallace, York.
Replacements: Stegman for Monye (28), Brooker for Gray (48), Bolt for Dickson (71).
Not used: Marfo, Sinckler, Matthews, Trayfoot, Clegg.
Referee: Chris White (RFU).