Division Two leaders Essex and bottom side Durham both had the better of the opening day of their County Championship matches as wickets tumbled.
Jamie Porter took 4-32 as Essex bowled out Gloucestershire for 76 at Chelmsford before an unbeaten 71 from Paul Walter helped the hosts to 150-5.
Durham dominated Glamorgan, dismissing the visitors for 97 and reaching 223-3 in reply as openers Michael Jones and Alex Lees both hit half-centuries.
Elsewhere, Jamie Smith scored a century as Surrey made 252 at Northamptonshire.
In Division Three, there was another 50 for veteran Kent all-rounder Darren Stevens against Worcestershire, and Leicestershire batted themselves into a strong position against Derbyshire.
Essex reduced Gloucestershire to 47-7 after winning the toss and deciding to bowl.
Porter led the way for the 2020 champions but Simon Harmer (3-2) and Sam Cook (3-27) played their part as the visitors were skittled after 28 overs - with Ryan Higgins top-scoring for the hosts with 25.
Essex slipped to 32-4 and 75-5 in reply before Walter and Adam Wheater (30 not out) enjoyed an unbroken stand of 75 for the sixth wicket, establishing a lead of 74 runs.
Glamorgan posted their lowest-ever Championship total against Durham after collapsing from 63-1 following the dismissal of Hamish Rutherford for 43 at Chester-le-Street.
Paul Coughlin took 4-11 as he made his return from injury, with Ben Raine and Chris Rushworth both picking up three wickets.
Durham openers Jones (81) and Lees (55) put on 119 for the first wicket, before David Bedingham reached 44 not out at stumps.
The hosts are already 126 runs ahead - and Bedingham will start day two just 11 runs short of becoming the first man to reach 1,000 County Championship runs for the season.
At Northampton, opener Cameron Steel and captain Hashim Amla both fell for ducks as the Surrey were reduced to 61-4, but Smith and Will Jacks (60) put on 155 for the fifth wicket to fight back.
Tom Taylor (5-41) and Ben Sanderson (4-32) starred for Northants, with Smith the last man to fall for 123 - an innings which included 17 fours and a six.
The hosts saw out three overs at the end of the day, closing on 7-0 in reply.
Worcestershire were reduced to 54-6 by Kent at Canterbury before Ben Cox (41 not out) and Joe Leach (38) restored some respectability for the table-toppers, who were eventually bowled out for 133, Nathan Gilchrist taking 5-38 and Matt Milnes 4-35.
"Matt Milnes is bowling like Dale Steyn at the moment," said Gilchrist. "You can't stop him."
Kent were in trouble at 22-3 in reply, but 50 from wicketkeeper Ollie Robinson got the visitors back on track, and Darren Stevens (56 not out) and Jack Leaning (52 not out) helped Kent to 184-4 at the close - a lead of 51 runs.
Leicestershire enjoyed a good day with the bat after winning the toss against Derbyshire.
After the losses of Hassan Azad and George Rhodes (54), Sam Evans (88) and Lewis Hill shared a third-wicket partnership of 139.
Hill was 86 not out at stumps, with Chris Wright alongside him on 13, as the Foxes closed on 282-3.
Day One scoreboards
Chelmsford: Gloucestershire 76 (Porter 4-32, Harmer 3-2) v Essex 150-5 (Walter 71*)
Chester-le-Street: Glamorgan 97 (Coughlin 4-11, Raine 3-25) v Durham 223-3 (Jones 81, Lees 55)
Northampton: Surrey 252 (Smith 123, Jacks 60; Taylor 5-41, Sanderson 4-32) v Northamptonshire 7-0
Canterbury: Worcestershire 133 (Cox 41*; Gilchrist 5-38, Milnes 4-35) v Kent 184-4 (Stevens 56*, Leaning 52*, Robinson 50; Pennington 3-39)
Derby: Leicestershire 282-3 (Evans 88, Hill 86*, Rhodes 54) v Derbyshire