Tom Lawes took five wickets as Surrey claimed three of the five points they need to be crowned county champions on the opening day against Hampshire at the Ageas Bowl.
All-rounder Lawes rolled through the Hampshire middle order for his third five-for of the season - worth five for 27 - with Kemar Roach picking up three for 41.
Hampshire battled to a below-par 219 around Ben Brown's positive 78 before Mohammad Abbas pinned back Surrey, who ended the day on 47 for two, a deficit of 172.
Essex, the only team who could capitalise on an unlikely Surrey collapse were hit by a superb innings from Rob Keogh for Northamptonshire at Wantage Road.
With his county already relegated, the 31-year-old put on a show with a stunning 154 off just 147 balls to claim his county's first batting bonus point at home all season.
In doing so Keogh passed 6,000 career first-class runs and became Northamptonshire's highest run scorer in the Championship this season as they closed on 279 for six.
Relegation-threatened Kent endured a frustrating opening day at Canterbury as Lancashire recovered from 18 for three and 240 for eight to reach 327 all out at stumps.
The hosts, who went into the final round one point ahead of Middlesex, made a bright start with early wickets for returning Matt Quinn and Nathan Gilchrist but their optimism was short-lived.
Josh Bohannon scored 113 and put on a crucial 121 for the fifth wicket with George Balderson, who made 54, to sustain Lancashire's hopes of a top-three finish.
No doubt with one eye on events at Canterbury, Middlesex - who have to better Kent's result or match it with at least one more bonus point than their rivals - closed a truncated opening day against Nottinghamshire on 162 for three.
Only 42 overs were possible after a rain-delayed start and it appears crucial that the partnership between Ryan Higgins (60) and John Simpson (26) turns into something substantial on day two.
Somerset were bailed out by their lower order as they reached 180 for eight on the first day against Warwickshire at Edgbaston.
After rain wiped out the first session, the visitors plummeted to 37 for six but
Neil Wagner (55 not out) and Josh Davey (28 not out) sparked a revival.
Graham Clark and David Bedingham both scored centuries as Division Two winners Durham piled on the runs looking to end the season with a victory over Leicestershire.
The visitors, who started with hopes of joining their hosts in Division One next season, chose to bowl and made early inroads when they dismissed Alex Lees for six.
However, Michael Jones and Scott Borthwick put on 99 for the second wicket and a subsequent 208-run partnership between Clark and Bedingham left the hosts well in control at 409 for five at close.
Derbyshire dominated the first day's play at Glamorgan as umpire Sue Redfern made history by becoming the first woman to stand as an umpire in a men's first-class match in England and Wales.
Luis Reece made an unbeaten 139 and it was Lloyd who confirmed the wickets of Harry Came and Brooke Guest as the visitors reached 308 for two, before Glamorgan responded with 22 without loss at stumps.
Kashif Ali picked the perfect time to post a career-best 93 as Worcestershire boosted their promotion hopes by reaching 280 for five on a truncated opening day of action at Headingley.
Kashif, 25, had only scored 98 runs in four previous appearances dating back to last summer, but stepped up when it mattered for his county, who require two more points to join Durham in claiming promotion.
Sixteen wickets fell on the first day at Sussex as Gloucestershire, chasing their first win of the season, reduced the hosts to 202 before closing the opening day on 136 for six.
