Quinnell, younger brother of Scott and Craig, scored two tries
Northampton: (0) 12
Tries: Hartley, Robinson
Worcester: (18) 24
Tries: Quinnell 2
Pens: Brown 4
Worcester put their poor opening to the Premiership behind them to claim their first win of the season in their EDF Energy Cup opener at Northampton.
The Warriors led through an early try from Gavin Quinnell, and the flanker grabbed a second before half-time.
Fly-half James Brown converted one and also kicked two penalties as the visitors led 18-0 at the interval.
Saints hooker Dylan Hartley grabbed a try on the resumption but two more Brown penalties took Worcester clear.
Scrum-half Mark Robinson did claim a second try for Saints late on but they will now need to win at Newport-Gwent Dragons next week and beat Leicester in their final group game to have any chance of progress.
Victory extended Worcester's remarkable recent record at Franklin's Gardens, this success their fourth in a row.
It was a memorable full debut for 22-stone Quinnell, younger brother of former Wales forwards Scott and Craig, after his arrival from Llanelli in the summer.
The 22-year-old twice bulldozed his way over before being replaced in the 52nd minute, and Worcester now have a good chance of qualifying with their next two pool games at home.
Worcester director of rugby John Brain:
"Gavin offers something different and has a lot of potential. If you're his size with his skills, you have to be in with a shout of playing representative rugby - provided he gets fit and he can do it over 60-80 minutes.
"The main problem in his career so far has been that nobody has bothered to condition him. He has changed body shape since coming to us and is probably capable of only playing 40 minutes.
"It's good to win. In the first half we played some good rugby. In the second
half we showed a lot of spirit and commitment in defence."
Northampton head coach Paul Grayson:
"It's an understatement to say we never got going. We were varying degrees of poor. To be scrapping around near the end for losing bonus points shows how bad we were.
"The preparation was good. It has been disrupted but you can't blame injury for the lack of physicality. We didn't function on any level as a team.
"That performance was painful from start to finish. We had no impetus, no go-forward and no one was carrying the ball."
Northampton: Kydd; Lamont, Wyles, Quinlan, Cohen; Myring, Vass; Emms, Richmond, Budgen; Lord, Short; Easter, Harding, Browne.
Replacements: Hartley, Tonga'uiha, Browne, Lewitt, Robinson, Diggin, Laird.
Worcester: Delport; Tucker, Avramovich, Whatling, Trueman; Brown, Powell; Taumoepeau, Gotting, Horsman; Blaze, Murphy; Quinnell, Collins, Horstmann (capt).
Replacements: Fortey, Lutui, Collier, Hickey, Runciman, Rasmussen, Oduoza.
Referee: D Richards (RFU)