Lancashire won to climb to the top of the table while Hampshire boosted their survival hopes and Yorkshire and Sussex played out a thrilling draw.
Lancashire are top after 13 games on 198 points as they beat a spirited Worcestershire side by 98 runs in Blackpool.
Steven Croft's 107 dragged the home side to 282 first time around as Gareth Andrew claimed 3-47 and Richard Jones 3-62.
Worcestershire were 21-5 before Ben Scott (65) and Andrew (61) guided them to 202. Glen Chapple took 4-47 and Saj Mahmood 3-39.
Lancashire fell from 184-3 to 248 all out despite Karl Brown's 85 and Croft's 50. Gareth Andrew took 5-59 for the visitors.
Chasing 329, Vikram Solanki's 107 gave them hope and despite being 203/5 at the end of Day Three and needing another 126 runs, they fell to 230 all out. Tom Smith claimed 4-32 and Gary Keedy 4-58 to give Lancashire victory by 98 runs.
Worcestershire are eighth on 106 points but have a game in hand over the counties just outside the relegation zone.
Durham are second after 13 games on 185 points.
The home side were 20/2 off eight overs after two days of the match before eventually being dismissed for 177 on Day Three. Andre Adams taking 6-33 and Luke Fletcher 3-52.
Nottinghamshire piled on 402-9 declared as Samit Patel hit 128 and Riki Wessels 82, before the match ended as a draw. Charl Willoughby picked up 4-76 for the home side.
Somerset are third after 13 games on 177 points and Nottinghamshire are fifth after 13 games on 145 points.
Warwickshire are fourth on 172 points and have a game in hand in the title-chase but lost their latest game to bottom side Hampshire by 209 runs at Edgbaston.
Hampshire could only make 141 first time around as Chris Woakes ran riot with 7-20.
Woakes then top-scored with 65 as the home side replied with 250. James Tomlinson's 3-71 the pick of the bowlers.
Hampshire posted 416 second time around as James Vince hit 145 and Sean Ervine 63. Boyd Rankin bagged 4-99 for the hosts.
They were eventually all out for just 98 to lose by 209 runs, as Tomlinson claimed 4-13, Chris Wood 3-36 and Imran Tahir 2-11.
Hampshire have now won two on the bounce but stay bottom on 85 points after 12 games.
Sixth placed Sussex and seventh placed Yorkshire played out one of the best County Championship draws for a long time in Scarborough as both counties scramble to avoid relegation.
Sussex slipped to 27-3 before Michael Yardy (130) and Ben Brown (107) rescued the visitors, as they made 398. Ryan Sidebottom claimed 5-53 and Rich Pyrah 3-64.
Yorkshire were indebted to Joe Root (160) and Gary Ballance (87) as they posted 388 in reply. Amjad Khan picked up 4-70 and Wayne Parnell 3-86.
Sussex reached 333-6 declared as Yardy (122) again hit a century and James Anyon made 53. Adil Rashid was the pick of the home sides bowlers with 4-121.
Yorkshire needed 344 from just 54 overs and when Jacques Rudolph smashed 120 from 125 balls in an opening stand of 187 the target looked on.
They were eventually just short on 312-6 at 5.77 runs per over as both sides had to settle for the draw.
With three games left each Sussex have 132 points and Yorkshire have 107.
The next round of games sees Nottinghamshire host Durham from August 22, Hampshire play Worcestershire and Yorkshire against Warwickshire from August 23.