With timing that had the England selectors smiling as broadly as supporters of Durham, Graham Onions tore into the Somerset batting with devastating consequences at Taunton, where the home side collapsed to 69 all out in reply to the champions' 543.
The 26-year-old pace bowler bowled Marcus Trescothick, then caught and bowled Arul Suppiah before dismissing James Hildreth, Craig Kieswetter, Peter Trego and David Stiff for ducks. He finished with 6 for 31 while team-mate Callum Thorp claimed three wickets for just five runs. England discard Steve Harmison took only one.
Following on at 83 for 1 at the close, it will take a supreme effort from them to require Durham, led to their position of strength by Dale Benkenstein's 181, to bat a second time.
Only Ashwell Prince, with 74, could offer significant resistance against Nottinghamshire at Old Trafford, where Lancashire, having opted to bat first, were dismissed for 189, seamer Andre Adams finishing with 4 for 49.
An 150-run partnership between Sean Ervine (109) and Nic Pothas (74) was at the heart of Hampshire's 341 for 8 after being asked to bat first by Sussex at the Rose Bowl.
In the Second Division, Phillip Hughes completed his second century in as many matches at Southgate, where Irishman Eoin Morgan joined in with an unbeaten 114 as Middlesex declared on 493 for 7. Steve Finn, the 20-year-old English pace prospect, has 3 for 42 in Leicestershire's 161 for 5 in reply.
Kent's decision to put Essex in at Chelmsford did not produce the desired outcome, the home side reaching 330 for 7 by the close.Reuse content