England captain Alastair Cook warmed up for the international summer with his first hundred of the season to steer Essex away from a precarious position on day two against Derbyshire.
The left-handed opener posted 139 not out - his first three-figure score since becoming a father and 46th of his first-class career - to give Essex a second-innings lead of 237 with five wickets remaining.
Cook's effort capped a brilliant fightback from the home side, who had earlier dismissed Derbyshire for 154 from their overnight 139-5 with Shivnarine Chanderpaul stranded on 75no.
Evergreen seamer David Masters took three morning wickets to end with figures of 6-46 and Cook then helped wipe out a 60-run first-innings deficit with a fluent knock at the top of the order.
He struck 17 boundaries and shared century stands with Tom Westley (56) and Ravi Bopara (48), however three late wickets for Tim Groenewald have kept the contest nicely poised at the halfway stage.
One man tipped to join Cook in the England side in future years, James Vince, also notched three figures to hand Hampshire maximum batting points and a healthy first-innings lead against Gloucestershire.
Vince treated the Bristol crowd to an exhibition in classical strokeplay to score 144, sharing a 155-run partnership with Adam Wheater (81no) as Hants ended the second day on 417-9 in reply to Gloucestershire's 304 all out.
Will Gidman (4-66) and Matt Taylor (4-75) both took four wickets for the struggling hosts.
Worcestershire's home clash with Kent is fascinatingly poised after the home side battled back with the ball on day two at New Road.
Kent fell from 127-3 to 229 all out in reply to Worcestershire's 224 as only Daniel Bell-Drummond (61) and Ben Harmison (55) managed to hold off the Pears attack for any length of time.
Worcestershire then made a strong start to their second innings, reaching stumps on 41-0 with in-form captain Daryl Mitchell (22no) and Matt Pardoe (18no) at the crease.