Tom Banton crafted a superb triple century as Somerset took control against Worcestershire on the second day of their County Championship Division One clash at Taunton.
The 26-year-old made the highest first-class score in the county's history with his 344 not out off 381 balls, with 53 fours and a six.
James Rew also hit a fine 152 in a fifth-wicket stand of 371 as Somerset closed on 637-6, a commanding first-innings lead of 483 runs.
Champions Surrey were again made to toil as Essex extended their advantage at Chelmsford.
After Essex resumed on 356-4, Matt Critchley completed an unbeaten 145 and wicketkeeper Michael Pepper made 109 as the hosts declared at 582-6.
In reply, Surrey had reached 109-1 at close, with captain Rory Burns 59 not out and Ollie Pope unbeaten on 45, trailing by 473 runs.
Newly-promoted Yorkshire struggled against Hampshire at the Utilita Bowl, though a half-century from captain Jonny Bairstow at least took them beyond the hosts' first-innings total.
Having been skittled out for 121 on day one with Hampshire making 164-5, Yorkshire fought back with the ball. Jack White and George Hill each finished with three wickets as the hosts were all out for 249, captain Ben Brown unbeaten on 49.
Bairstow, out for 10 in the first innings, returned his 56 off 108 balls, with opener Adam Lyth 57 not out as the visitors closed 61 ahead on 189-6.
At Trent Bridge, Nottinghamshire responded well to Durham's 378.
The visitors added only eight to their overnight 370-9 as Fergus O'Neill finished with 5-81.
In reply, Ben Slater's 92 and 79 from Freddie McCann helped Nottinghamshire reach 297-5.
Sussex piled up 528 against Warwickshire, who replied impressively but still trailed by 305 runs at the close.
Visiting captain John Simpson turned his 116 overnight at Edgbaston into 181 not out but Warwickshire ended the day at 223-3, with opener Rob Yates unbeaten on 113.
Watch England's home summer live on SportNews, starting with the four-day Test against Zimbabwe at Trent Bridge in Nottingham from May 22.
