Warwickshire put their title aspirations back on track but Durham lost again, while the battle against relegation looks like it will go down to the final game.
Lancashire remain on top with 198 points after 13 games.
Warwickshire climbed to second on 195 points after 13 games as they beat Yorkshire by an innings and 58 runs at Headingley.
Yorkshire posted 297 the first time around as Gary Ballance hit 57. Keith Barker took 4-73 and Chris Metters 3-31.
Shiv Chanderpaul's 193, with Barker's 85 and Tim Ambrose making 66, guided the away side to 482. Joe Root claimed 3-33 and David Wainwright 3-111.
Yorkshire slumped to 25-4 and never fully recovered as they were dismissed for 127. Rich Pyrah's 28 was the top score as Chris Wright picked up 5-31 and Keith Barker 4-56 to give Warwickshire the victory by an innings and 58 runs.
Yorkshire are eighth after 14 games on 111 points and occupy the final relegation place.
Durham have lost three of their last four games after a 67-run defeat against Nottinghamshire at Trent Bridge.
Durham were soon in trouble at 44-4 before recovering to post 195. Blackwell hit 52 and Dale Benkenstein made 49. Graeme White claimed 3-19 and Andre Adams 3-61.
Nottinghamshire made 245 the second time around, thanks to Riki Wessels's 84 and Adams's 53 not out. Claydon was the pick of the bowlers with 5-54.
Chasing 321 for victory, Durham fell to 35-3 but Mark Stoneman's 74 and lower order runs kept them in the hunt, but they eventually fell just 67 runs short. Graeme White took 4-72 and Adams 3-54 for the home side.
Durham are third after 14 games on 188 points and Nottinghamshire are fifth after 14 games on 166 points.
Worcestershire are one place above the relegation zone with 13 games on 113 points after they drew with Hampshire at the Rose Bowl.
Hampshire were bowled out for just 179 in their first innings, with Gareth Andrew (3-28), Alan Richardson (3-37) and Richard Jones (3-38) doing the damage.
Worcestershire slipped from 135-1 to 204, despite Vikram Solanki's unbeaten 79. Imran Tahir claimed 5-29 and Chris Wood 4-35.
The home side were in trouble again at 78-6, but an unbroken stand of 79 between Chris Wood (56 not out) and Dimi Mascarenhas (25 not out) guided them to 157-6, and the match was ended as a draw. Kemar Roach picked up 2-41 for the away side.
Hampshire stretched their unbeaten run to five games but remain bottom after 13 games on 91 points.
The next round of fixtures, from August 31, sees Somerset against Hampshire, Susses versus Durham, Warwickshire take on Yorkshire and Worcestershire play Lancashire.