Gloucestershire posted 268 (van Buuren 76, Guthrie 4-50) and 264 for 7 (Bracey 75*, Bancroft 64, Guthrie 3-59) while Northamptonshire were dismissed for 465, losing by 67 runs.
The left-arm seamer, who posted a career‑best 52 with the bat earlier, took 4/50 to bowl the opposition out for 268 in their first innings and then claimed three more wickets after enforcing a follow‑on.
Gloucestershire fought to finish on 264 for 7, but they will need a standout performance on the final day to avoid a sixth loss in seven matches.
Needing 83 to avoid the follow‑on, Gloucestershire’s hopes were dented when Graeme van Buuren, having added only a single to his overnight 75, lofted Saif Zaib’s wayward full toss to backward square.
The other unbeaten batter, Jack Taylor, then edged a catch to mid‑on in Zaib’s next over; although he had initially declined a second new ball, Northamptonshire’s decision to change the ball four overs later proved decisive.
Guthrie opened his day by bowling Daz Ahmed on the pads — perhaps marginally high — and followed with an inswinger that crashed into Matt Taylor’s off stump. Kristian Clarke, having scored a competent 21, then faced Harry Conway’s delivery, prompting Gloucestershire’s openers to don their pads once more.
Bancroft and Joe Phillips kicked off the second innings with a brisk 4‑run‑per‑over partnership, the captain lofting Raphy Weatherall for a six over cover before adding a leg‑side four that lifted the team’s total to 50 before lunch.
Bancroft completed his half‑century in the afternoon, but Phillips was dismissed caught behind outside off stump, and Ricardo Vasconcelos subsequently took a low catch to remove Tommy Boorman.
Luke Procter bowled a probing spell from the David Capel end, beating the bat and narrowly missing a wicket when Miles Hammond’s edge skidded past George Bartlett at third slip.
When Procter was replaced by Guthrie, the left‑arm bowler’s second delivery beat Hammond and the ball popped into Bartlett’s hands after he had moved to gully. Guthrie then dismissed Bancroft, who edged to second slip, and a subsequent tactical change yielded Northamptonshire’s fifth wicket as van Buuren was bowled by James Sales’s first delivery.
Bracey stayed resolute, timing his shots expertly as he leg‑glanced Conway for four and then drove him for a boundary, securing his second half‑century in as many days. He later lost Jack Taylor, caught by Guthrie after a pull to deep mid‑wicket, yet Clarke added a useful 22, guiding Sales to the rope at third man and putting Gloucestershire in a strong position.
Sales threatened to dismiss Bracey, edging the ball, but Vasconcelos fumbled the chance as he dived in front of the slips, and Ahmed slowed Northamptonshire’s momentum by hitting Calvin Harrison for six, finishing on 28.