Blackwell builds on solid start provided by Di Venuto
Champions Durham, looking for their first win of the season, made a serene start in reply to Hampshire's 345 at Chester-le-Street, where Ian Blackwell's innings of 83 tilted an evenly-balanced contest.
Opener Michael Di Venuto had earlier posted 71 runs as Durham coasted to 284-5.
Hampshire, 298-8 overnight, added another 47 yesterday morning, with Danny Briggs last man out for 28 to give Liam Plunkett his fourth wicket.
James Anderson added two more wickets to Wednesday's six-wicket haul as Essex endured a dismal start to their second innings against Lancashire, closing on 46-2.
Earlier, Paul Horton registered a century and his 123 was added to by Steven Croft (56) and Stephen Moore (61) as they helped Lancashire to 312 all out, 133 ahead of the hosts' first-innings effort.
A devastating spell of bowling from Stuart Broad put Nottinghamshire in charge of their match with Somerset. The England all-rounder took five wickets in 27 balls as Somerset collapsed to 43-6 in their second innings.
Earlier, Paul Franks (61) and Hashim Amla (58) helped the hosts to 250 all out before Broad swiftly made inroads into Somerset's batting order to finish with 5-59 from 11 overs. Marcus Trescothick was 63 not out as the visitors reached 120-6 at the close.
Robin Martin-Jenkins's century put Division Two leaders Sussex in a strong position at Bristol.
The 34-year-old scored 102 as his side reached 302 in their second innings, setting Gloucestershire an unlikely 327 to win. The home side closed at 12-1.
A third-wicket partnership of 223 between Vikram Solanki and Moeen Ali enabled Worcestershire to recover from the shock of losing two wickets without a run on the board in the face of an intimidating Surrey total of 493. Worcestershire closed on 262-3.
John Simpson's maiden first-class century and two wickets from Danny Evans put Middlesex in a commanding position as they declared on 442-8 against Northamptonshire at Wantage Road.
The hosts were struggling on 178-4, 264 runs behind.
Glamorgan's satisfaction at removing Derbyshire batting star Chris Rogers swiftly evaporated as Greg Smith marked his 100th first-class innings with a century.
Smith and Garry Park shared a fifth-wicket stand of 156 to help Derbyshire recover from 65-4. By the close, Smith's unbeaten 121 had lifted Derbyshire to 285-9, a lead of 13.