In Division One Sussex's Steve Magoffin ripped through Somerset's normally prolific line-up, while in the second tier, old-stager Alan Richardson did the same to Gloucestershire as Worcestershire impressed.
Despite the action elsewhere, Magoffin's eight for 20 off 11 overs was comfortably the best bowling performance of the day, if not the season so far. The Australian cut Somerset to ribbons as only three men made double figures in an all-out total of 76.
In response, Alfonso Thomas took four Sussex wickets and the rest were shared out amongst Peter Trego and Steve Kirby, but 77 from Rory Hamilton-Brown and 46 from Chris Nash gave them a resting total of 298 for nine - an overall lead of 222.
The other game in the top tier saw Durham make 259 against Middlesex and then reduce their visitors to 11 for two at the close.
Phil Mustard (62) and Scott Borthwick (52) both passed 50 for Durham as Corey Collymore (four for 61) helped himself.
In response, Graham Onions and Callum Thorp took a wicket each, with the later removing the in-form Chris Rogers for just three.
Worcestershire's evergreen paceman Alan Richardson continued his rich vein of form with a career-best eight for 37 against Gloucestershire in the LV= County Championship Division Two match at New Road.
The 38-year-old ripped through the visitors who were all out for 234 in 70.3 overs and, at the close, the hosts' reply was 65 without loss off 23 overs with skipper Daryl Mitchell unbeaten on 46.
Gloucestershire had no answer to deadly Richardson who has taken 20 wickets in six days after his first four Championship games this season had yielded just six for 282 runs.
It was the third eight-wicket haul of his career - and his second against Gloucestershire - which eclipsed his previous best return of eight for 46 for Warwickshire against Sussex at Edgbaston in 2002.
Elsewhere in Division Two, on the second day of play between Leicestershire and Glamorgan at Grace Road, the home side were in all kinds of trouble at stumps.
Starting the day on 256 for five, Glamorgan were eventually bowled out for 442, with James Allenby ending unbeaten on a brilliant 138.
Graham Wagg offered ample support with 58 and then took one of the 10 Leicestershire wickets that fell for 142 - with Michael Hogan and John Glover equally sharing eight of them.
Plenty of wickets fell at Canterbury too - 11 in total - as Kent knocked over Essex for 212 and then ended the day on 20 for one.
Only a seventh-wicket stand of 88 between James Foster (47) and Graham Napier (58) gave Essex a fighting chance as Darren Stevens (four for 36) shone. It was Napier's fifth half-century in eight innings.