A second day in which 17 wickets fell at the Emirates Durham ICG left Durham in a strong position to register their first win of the LV= County Championship season.
England-capped seamer Graham Onions and Chris Rushworth claimed four victims apiece as Somerset were skittled for 185 and the hosts extended a first-innings lead of 123 runs to 275.
They were 152 for seven at stumps as Peter Trego, fresh from a battling 48 which put the brakes on his side's terminal batting decline, took his tally to six wickets for the match with another three.
Having dismissed Durham for 308 on the opening day, Somerset would have had high hopes of narrowing the gap, if not surpassing it, when resuming on seven without loss.
But the early departure of captain Marcus Trescothick, chopping on one which nipped back from Onions, set the tone.
From 24 without loss they slipped to 84 for five and only Trego's 79-run stand with Craig Kieswetter, who made 35, prevented a premature conclusion to the innings.
The return of Onions after lunch provided the breakthrough again as Trego was pinned leg before to end a 41-ball knock which included a six and six fours.
WICKET: Trescothick plays on to a @BunnyOnions delivery that nips back from outside off...Somerset 24/1
— Durham Cricket Club (@DurhamCricket) April 21, 2014
Kieswetter followed next, feathering a thin edge to wicketkeeper Phil Mustard off Rushworth, and when Nick Compton, batting down the order at eight after suffering neck spasms, was last man out to a sixth lbw decision in the last seven wickets to fall, Somerset were all out for 185.
Such a substantial first-innings lead gave Durham more freedom to press home their advantage and, after losing Mark Stoneman and Scott Borthwick, the latter to a brilliant one-handed catch from Chris Jones at short midwicket, Keaton Jennings and Michael Richardson put on 57 for the third wicket either side of tea.
Durham's lead was 211 when Richardson pulled Jamie Overton straight to Lewis Gregory at midwicket to depart for 32.
But Jennings' dismissal for 41, edging an attempted drive to Trescothick off spinner Johann Myburgh, was quickly followed by those of Mustard and Gareth Breese, who fell in consecutive balls to Trego.
Although Usman Arshad managed to survive the hat-trick ball he did not stay around much longer, departing in the next over.
Captain Paul Collingwood and Jamie Harrison, on 23 and 16 respectively, ensured no further losses in guiding their side to the close.