Lancashire won a thrilling Roses encounter to lead Division One, while Durham, Warwickshire and Sussex all won in this round.
Lancashire beat Yorkshire by six wickets with four balls to spare in a rain-affected encounter at Liverpool.
Yorkshire were bundled out for 141 in their first innings, despite Joe Sayers's 53. Gary Keedy (4-44) and Farveez Marharoof (4-35) did the damage.
Paul Horton hit 93 and Mark Chilton 77 as Lancashire made 329 in reply. Steven Patterson's 4-51 was the pick of the Yorkshire bowlers.
The away side were looking set to draw the game on 278-4 but collapsed to 308 all out. The hard work by Sayers 232-ball 75, 60 from Andrew Gale and half-centuries from Gary Ballance (57) and Adil Rashid (52) was undone by Keedy's 6-133.
Chasing 121 from 15 overs, Lancashire re-shuffled their batting order, and it worked as Maharoof hit 31 not out from 19 balls to give the home side victory with only four balls remaining.
Durham are second after condemning Worcestershire to their sixth successive county championship defeat, this time by an innings and 57 runs at the County Ground.
Durham piled on 587-7 declared as Gordon Muchall hit 175, Ian Blackwell hit 134 and Phil Mustard hit 101.
The home side were asked to follow on without Adrian Shankar, who had retired hurt in the first innings. They performed better but were still dismissed for 345, Ben Scott hitting 73, Moeen Ali 63, Vikram Solanki 58 and Gareth Andrew 50.
Harmison took 3-84, Blackwell 2-73 and Steve Borthwick 2-53 as Durham climb to second in the table.
Warwickshire beat current holders Nottinghamshire by nine wickets at Trent Bridge to climb to third in the league and send Nottinghamshire to fourth.
Ian Bell's 139 guided the away side to 376, while Stuart Broad (3-92) and Andre Adams (3-111) were among the wickets.
Nottinghamshire subsided to 117 as the away side's four bowlers all took wickets. Darren Maddy's 3-29 the pick of the figures.
Following on, the home side were in trouble again at 40-4 but Paul Franks's 96, Adam Voges 74 and Andre Adams's 51 from 35 balls dragged them up to 318.
Sussex are up to fifth after they beat Somerset, who slip to sixth, by eight wickets.
Somerset posted 213 in their first innings, and Marcus Trescothick was the top scorer with 63. Sussex only used three bowlers, but they did the job, and Rana Naved's 5-79 was the pick of the attack.
Sussex slipped to 95-8 before they recovered to post 177 thanks to James Anyon's 51. Peter Trego picked up 4-24 and Steve Kirby picked up 3-54.
Trescothick (79) again led the way for his Somerset teammates, but they were dismissed for 235, Rana Naved's 5-82 restricting the away side.
Chasing a tricky target of 272 in a low-scoring game proved no problem for Sussex who finished 275-2 from 68.4 overs to wrap up a eight-wicket win and their third victory of the season.
From May 24 Hampshire face Lancashire, in the match between the only two sides to have played just five games, Somerset play Yorkshire and Warwickshire host Durham.