England captain Joe Root fell agonisingly short of scoring a second successive Specsavers County Championship century – but his brother Billy reached three figures as the second round of matches began.
Joe Root followed up his unbeaten ton in the drawn game against Division One opponents Nottinghamshire earlier this week by hitting 94 as Yorkshire closed on 310 for three against Hampshire at the Ageas Bowl.
Billy, meanwhile, marked his championship debut for Glamorgan with an unbeaten 126 in their Division Two clash against Northamptonshire.
The England skipper compiled a third-wicket stand of 182 with Gary Ballance, who strengthened claims of a possible England recall by posting a second championship century of the season, ending the day on 120 not out. Opener Adam Lyth also scored 67.
Thirteen wickets fell on the opening day at Trent Bridge, where Somerset's Lewis Gregory continued his fine start to the season by taking six for 68 as Nottinghamshire were dismissed for 263 – with Chris Nash top-scoring on 58.
Stuart Broad then removed Somerset openers Marcus Trescothick and Azhar Ali as the visitors reached 74 for three in reply, trailing by 189 runs.
Surrey made a strong start to their championship title defence at the Kia Oval, finishing the day on 342 for seven against Essex after wicketkeeper Ben Foakes sparked a fightback following three wickets falling quickly before lunch.
Foakes' 69 included 11 boundaries, while Will Jacks made 88 and Ryan Patel an unbeaten 70. Australian Peter Siddle was the pick of Essex's bowlers, taking four for 82.
There were also plenty of runs at Edgbaston, where Zak Crawley's 108 – his second first-class century – underpinned Kent's 367 for five against Warwickshire.
Crawley received strong support from Heino Kuhn (72) and Ollie Robinson (59) as a Warwickshire attack minus injured trio Chris Woakes, Olly Stone and Liam Norwell found it hard going.
Cameron Bancroft endured a testing first day as Durham captain against Division Two opponents Sussex.
Australian Bancroft's career was put on hold in March last year when he was given a nine-month suspension by Cricket Australia for attempting to manipulate the ball with sandpaper during a Test against South Africa in Cape Town.
Bancroft was then signed by Durham, but runs proved hard to come by as his team laboured to 210 for eight at the Emirates Riverside, with Bancroft making 33 off 159 balls during just over three hours at the crease.
There was no run drought in Cardiff, though, where Billy Root's century was one of three for Glamorgan's batsmen as they racked up 433 for four at Northants' expense.
Marnus Labuschagne hit 121, making it the first time in Glamorgan's history for two players on debut to score hundreds in the same match, and there was also an unbeaten 101 from 103 balls from Kiran Carlson.
Worcestershire, put in to bat by Leicestershire at Grace Road, capitalised in impressive fashion as centuries from Daryl Mitchell (114) and Hamish Rutherford (116 not out) saw the visitors reach 348 for four.
England paceman James Anderson took his first County Championship wickets at Lord's for 16 years as Lancashire reduced Middlesex to 236 for nine.
Anderson returned figures of three for 41, and Tom Bailey claimed four for 51 as Middlesex struggled despite dogged half-centuries from Stevie Eskinazi and Nick Gubbins.
And Tom Lace hit a career-best 83 as Derbyshire reached 256 for seven against Gloucestershire at Bristol, with solid support being provided by Harvey Hosein (41), Luis Reece (39) and Matt Critchley (34).
