Northants elected to field first and chipped away with regular wickets as Keaton Jennings, Cameron Steel and Graham Clark were all dismissed for 20.
Buck's haul also included the wickets of in-form Paul Collingwood and top-scorer Michael Richardson (27).
Barry McCarthy took 2-20 as Durham hit back, but Northants finished the day 59-3, 107 runs behind.
Division Two's bottom side Durham went into the game on the back of a dramatic defeat by Glamorgan and their fragile batting line-up was exposed by Northants' seam attack in an innings which lasted just 45.2 overs.
Northants lost Rob Newton, Alex Wakeley and Rob Keogh cheaply in reply, but Max Holden (19 not out) and Chesney Hughes (16 not out) prevented further damage before bad light brought an early close.
Former Derbyshire and Leeward Islands batsman Hughes, who played as a 'guest' for Northants in their tour game against South Africa A, is making his first Championship appearance since last August, on a non-contract, pay-as-you-play basis.
Nathan Buck took a career-best 6-34 to help bowl Durham out for 166 and give Northants the upper hand on day one.