|Bath (10) 22|
|Try: Chudley, Ewels, Mercer Con: Priestland 2 Pen: Priestland|
|Northampton (8) 13|
|Try: Hutchinson, Wood Pen: Grayson|
Bath survived conceding a try inside the opening minute and a red card to end Northampton's unbeaten start.
Rory Hutchinson charged down Rhys Priestland's kick to score early and James Grayson's penalty put Saints 8-0 up after as many minutes.
Bath fought back through Will Chudley's try and a Priestland penalty put them ahead at the break.
Aled Brew saw red before Charlie Ewels and Zach Mercer crossed either side of Tom Wood's finish.
Bath started the game at the bottom of the table, with Saints on top, and it was the visitors who took the early advantage.
Hutchinson charged down Priestland's clearance before kicking-on and grounding the ball.
The hosts hit back after 15 minutes when Chudley scampered over and Priestland put Bath into the lead for the first time just after the half-hour mark.
Welsh winger Brew was dismissed by Ian Tempest after 48 minutes for a high, off-the-ball challenge on Saints full-back George Furbank.
But despite being a man down, Bath held the upper-hand up front and Ewels crashed over from a driving maul just two minutes after Brew departed.
Wood reduced the gap to two points but Bath's pack won a string of penalties before Zach Mercer peeled off the base of a scrum to go under the posts.
Bath director of rugby Stuart Hooper told BBC Radio Bristol:
"We had to restart the game (after the early try). That happens, but credit to players, Saints have been the best attacking team in the Premiership so to limit them after that was outstanding.
"We had a plan for this game and it unfolded exactly as planned.
"I'll have to take another look at it but I am dubious about the red card. Slow motion and real time are very different things. There's protection of yourself as well as the other player.
"The other lads dug in and the effort they put in for each other was outstanding. The guys have been working hard in the scrum since June 24 as we know it's the cornerstone of Premiership campaigns."
Northampton director of rugby Chris Boyd:
"For Bath, credit to them, they've come away with a victory and the points.
"We're disappointed not to get anything out of the game. I always knew it was going to be an arm wrestle and tough down here.
"We just showed a bit of inconsistency and a bit of sloppiness around our execution."
Bath: Burns; Rokoduguni, Wright, Roberts, Brew; Priestland, Chudley; Obano, Dunn, Stuart; McNally, Ewels, Ellis, Bayliss, Mercer.
Replacements: Walker, Boyce, Judge, Stooke, Williams, Cook, Willison, Hamer-Webb.
Northampton Saints: Furbank; Collins, Dingwall, Hutchinson, Naiyaravoro; Grayson, Taylor, Franks, Haywood, Painter; Ribbans, Moon, Wood, Gibson, Harrison.
Replacements: Fish; Trinder, Hill, Ratuniyarawa, Coles, Mitchell, Strachan, Tuala,
Referee: Ian Tempest.