Flanker Samu Manoa's 70th-minute try - he was driven over the line by his fellow forwards just seconds after Worcester's former Northampton flanker Neil Best received a yellow card - made the difference before referee Greg Garner awarded Saints a late penalty try.
It was only Saints' second win in their last five league games, but it took them into fifth spot, one point above Gloucester, who tackle Wasps on Sunday.
Hooker Hartley and lock Lawes were punished for killing the ball and a late challenge, respectively, yet Northampton had enough in the tank to prevail.
Northampton fly-half Stephen Myler kicked five penalties and a conversion for a 17-point haul, while his opposite Andy Goode landed six penalties out of seven, but it was not enough to stave off Warriors' fourth successive Premiership defeat.
- Sports & Recreation