IT took until the 13th over to make the breakthrough, but Durham suddenly took four wickets in five overs and had Somerset wobbling on 117 for five at lunch.
There were three wickets for Graham Onions, who will have impressed watching national selector James Whitaker, and one each for Chris Rushworth and Jamie Harrison.
Nick Compton has yet to come in following a neck spasm, but Somerset do expect him to bat.
On a bright morning conditions looked good for batting, but the excellence of Onions and Rushworth has shown the wayward Somerset seamers what can be achieved.
Marcus Trescothick never looked comfortable and scored most of his 17 runs off the edge before he shaped to run Onions behind square on the off side and chopped on.
South African Test batsman Alviro Petersen stroked a couple of fine shots before he played back defensively to a good ball from Rushworth and edged low to Scott Borthwick at second slip.
In the next over Onions nipped one back to take out Chris Jones’ middle stump and something similar had James Hildreth lbw for a duck.
That made it 43 for four and Johann Myburgh could have been run out without scoring. He pushed to cover and was well down the pitch when Craig Kieswetter sent him back.
After the throw went to backward square leg they decided on a run and Myburgh would have gone had the shy at the non-striker’s end hit the stumps. Instead he profited from four overthrows and went on to make 22 before Harrison had him lbw with an in-swinger.
Durham were convinced they had Peter Trego caught behind next ball and he continued to live dangerously as he reached 22 at lunch with Kieswetter on 20.