Jordan Cox celebrated his elevation to the England squad with an unbeaten 184 in Essex's Rothesay County Championship clash with Leicestershire.
The 25-year-old, who has been added to the party for the second Test against New Zealand, raced to three figures off just 73 balls at Grace Road as the visitors finished day one 342-5 with Matt Critchley falling just three runs short of a century of his own.
Cox will resume tomorrow morning having struck 24 fours and two sixes so far in the 177 deliveries he has faced.
Opener Jordan Hermann's century helped Somerset reach 295-7 against Division One leaders Nottinghamshire at Trent Bridge.
Hermann made 106 before he became one of Fergus O'Neill's three victims, and 68 from Thomas Rew coupled with Archie Vaughan's 51 not out capped an encouraging day for the visitors.
Sussex trailed Glamorgan by just 19 runs with eight wickets in hand at the close of play at Hove.
Opener Daniel Hughes will resume on 48 not out with the hosts having made 136-2 in reply to the Welsh side's total of 155 all out in which Jaydev Unadkat took 4-29.
Will Luxton's brilliant 167 eased Yorkshire to 386-6 at stumps as Warwickshire's bowlers toiled at Scarborough.
Luxton, supported by Sam Whiteman (55) and Jonny Bairstow (49 n/o), batted the home side into a commanding position going into day two.
Nathan McSweeney and Saif Zaib mounted a fourth-wicket stand of 261 to give Northamptonshire the upper hand in their Division Two clash with Gloucestershire at Wantage Road.
McSweeney made 117 while Zaib hit 142 from a total of 380-7 after the hosts had been reduced to 41-3, with Kristian Clarke taking 5-81.
Liam Livingstone led the way with a five-wicket haul as Lancashire bowled out Kent for just 178 on the opening day at Blackpool.
Livingstone's 5-55 was the main contribution to a bowling effort in which James Anderson and Tom Bailey took two wickets each, with opener Ben Dawkins' 54 the only score of note for Kent
However, the home side ended the day uncomfortably on 17-2 after Keith Dudgeon removed openers Keaton Jennings and Harry Singh at a cost of just five runs off his four overs.
Graham Clark made a half-century as Durham's batters repeatedly failed to build upon solid starts to close on 302-7 against Derbyshire at Chester-le-Street.
All of the top six in the hosts' batting order made it to 25 but only Clark went past 50 - he fell one run later - as Ben Aitchison took 4-57.
Skipper Leus du Plooy top-scored with 85 as Middlesex closed on 291-8 at Worcestershire.
Opener Sam Robson got the visitors off to a positive start with a knock of 70, but wickets fell at regular intervals with Adam Finch taking 4-70 and Ben Allison 3-69.
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