Bath shrugged off the dismissal of wing Aled Brew early in the second half to topple the Premiership's early pacesetters with a powerful scrummaging display in a 22-13 win over Northampton.
The visitors could not have had a better start, being gifted a try after just 64 seconds. Priestland hesitated getting his clearance kick away and Grayson's charge-down left Scotland centre Rory Hutchinson with a simple hack-on to score.
Grayson missed the conversion but added a ninth minute penalty when Bath could easily have conceded a second try.
The home scrum had a clear edge however and a penalty from the put-in provided the platform for Bath's first score. Burns made a telling entry from full-back before Tom Ellis revived the attack in midfield and scrum-half Chudley spied a gap and sped 30 metres to touch down, with Priestland converting.
Saints continued to stretch Bath on the flanks with their quickfire rucks but Bath's scrum remained a potent weapon.
As the visitors began to find themselves on the wrong side of the penalty count, Priestland was on target again from nearly 40 metres to grab a 10-8 lead. That they held it to half-time owed a lot to Burns and his defensive work at full-back.
Soon after the break, Grayson wasted a chance to regain the advantage from the tee and Bath also repelled Saints' catch and drive from a line-out.
Brew's collision with George Furbank looked fairly innocuous at first, although the Saints fullback was sent sprawling. But replays showed the Bath wing's forearm had been dangerously high and the home side were down to 14 men for the remaining 33 minutes.
The red card galvanised them into a second try within four minutes as Stuart finished off a line-out catch-and-drive, but Priestland's conversion struck the bar.
Grayson's missed conversion left Bath with a two-point lead and then loosehead Ben Franks's yellow card evened up the numbers on the field. The two packs then spent six minutes fighting over the same patch of ground as Saints conceded two free kicks and three penalties in succession, with replacement loosehead Paul Hill following Franks to the sin-bin.
And referee Ian Tempest was playing advantage again when number eight Mercer scored off the scrum for Priestland to convert. By the final whistle, virtually every scrum was a penalty to Bath.