Steven Finn took four wickets to spearhead a second day Middlesex thrust with the ball as Somerset slipped to 185 for eight in their LV= County Championship Division One match at Northwood.
Marcus Trescothick and Tom Abell had put on a battling 76 for the first wicket in reply to Middlesex's 283, but Finn took two of four wickets to fall for 41 runs as Somerset slipped to 185 for eight at the close.
Mark Stoneman hit his second consecutive century for Durham, but the hosts were pegged back by some dogged Warwickshire fielding at Chester-le-Street.
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Stoneman's stand of 153 with Scott Borthwick took the score to 184 for one, but Durham were all out for 314 - with Rikki Clarke taking five wickets for 62 runs.
In four overs before close of play, the depleted visitors' line-up fashioned 10 without loss in response.
In Division Two, a late burst by Jesse Ryder kept Glamorgan at bay after they had restricted hosts Essex to 279 all out at Chelmsford.
Despite a half-century for opener Jaik Mickleburgh Essex failed to full capitalise on their promising start with Michael Hogan starring for the visitors as he took four wickets for 36 runs.
But Ryder responded in fine style to curtail the Glamorgan response, removing William Bragg via a catch from James Foster for three, then taking both Aneurin Donald and Andrew Salter lbw to leave the visitors on 40 for three at close of play.