Durham 163 for 3 (Stoneman 78*) trail Somerset 458 (Compton 166) by 295 runs
Nick Compton was dismissed for 166 but failed to pick up the tempo on day two at Taunton as Somerset missed out on maximum batting points. But a wicket with the last ball of the day put them in a very strong position against Durham.
Resuming on 139, Compton had batted for seven hours when he edged a catch behind off young offspinner Ryan Buckley, who finished with 3 for 128. Peter Trego with 42, George Dockrell's 31 and 24 from Jamie Overton provided valuable support.
By the close Durham had replied with 163 for 3, Scott Borthwick making 56 and Mark Stoneman an unbeaten 78.
Somerset began the day on 336 for 5 off 98 overs, with 12 more to get to the 400 mark and claim maximum batting bonus points. They only managed to reach 379 by the end of the 110th over, paying the price for a lack of acceleration as Compton, in particular, declined to change the pace of his innings from the first day.
He had faced 324 balls and hit 18 fours and a six when he was surprised by a bit of lift from Buckley and wicketkeeper Phil Mustard took the catch, the ball sticking between his legs.
That was 390 for 6 and with only five more added, Trego, unbeaten on 14 overnight, became another victim for Buckley, well caught by Paul Collingwood at full stretch at slip after edging the ball over Mustard's head.
Craig Meschede made only 12 before being caught behind off Mark Wood, who showed a lot of heart in the conditions to claim two for 89 from 29 overs.
It was 432 for 8 at lunch after which Overton was caught at point off Borthwick, who followed up next ball by dismissing Dockrell for his highest score for Somerset. He faced 50 balls and hit three fours and a six.
The promising Overton made the breakthrough when Durham replied, having Keaton Jennings picked up by James Hildreth in the slips for 15 with the total on 38.
But Stoneman breezed to his half-century off just 53 balls, with 11 fours, and found an equally aggressive partner in Borthwick. He followed Stoneman to fifty off 57 deliveries and it was a surprise when he was caught at short cover off Dockrell to reward the left-arm spinner for changing to the Old Pavilion End.
There was a bonus for Somerset off the last ball of the day as Will Smith, on 7, drove Overton carelessly straight to Gemaal Hussain at mid-off, who held a waist-high catch.