It was the Warriors' first away victory over the season and it boosted their survival bid while plunging Saints into a full-blown crisis.
The only try of the match came from Worcester's Giscard Pieters in the first half and the visitors had to hang on grimly, especially in the second period, as Northampton threw the kitchen sink at them.
Ultimately, though, the Saints could not break through Worcester's dogged defence while the Warriors' set-piece caused the Saints problems all afternoon.
Worcester went into the game shorn of James Brown because of a neck injury and that gave fly-half Tommy Hayes the chance to redeem himself after a poor couple of displays.
The former Cook Islands international, however, looked back to his best as he stroked home a second minute penalty to put the Warriors in front.
Northampton, who had lost seven Premiership games in succession before kick-off, looked nervy and their early knock-ons gave Worcester a massive confidence boost.
Following one of those Saints' mistakes, Hayes just missed with a drop goal attempt as the visitors began to dictate the pace.
Northampton, though, always looked a threat with fullback Bruce Reihana in full flight and, after sustained pressure, Paul Grayson's penalty pulled them level.
The Saints' period of parity did not last long. Springbok Thinus Delport set up another Worcester attack and a high tackle on Pat Sanderson gave Hayes the chance to make it 6-3 which he did with ease.
Northampton responded by launching attack after attack on the Worcester line but the Warriors took all the Saints could throw at them and responded with interest.
South African flyer Pieters, in only his second Worcester game, went in on the left following a flowing move and the Premiership's bottom side were 11-3 up with 29 minutes on the clock.
The Saints had their chances to score before the break but some slow ball and bizarre decision making gave Worcester a lift at half time as they went in ahead.
After much huffing and puffing, the home side dragged themselves back into the match with a Grayson penalty on the hour.
However, man-of-the-match Hayes was twice on hand to deny Northampton with two stunning tackles.
And, after repelling the Saints again, Hayes struck home a drop goal to extend Worcester's advantage with nine minutes left.
Replacement Shane Drahm had a late chance to resuscitate his side but his penalty agonisingly hit the post. It summed up the Saints' day as the 11,208 crowd began to trudge home disconsolately.
Hayes then capped a splendid display by landing his third penalty, with three minutes to go, to rub salt into the Saints' wounds.
If Northampton did not know they were in a relegation dogfight before today, Worcester's win will have well and truly set the alarm bells ringing around Franklin's Gardens.
For Northampton:Pens: Grayson 2
For Worcester:Try: PietersPens: Hayes 3DG: Hayes