Joe Clarke marked his debut for Nottinghamshire with an unbeaten century as the new Specsavers County Championship got under way.
The 22-year-old, who joined the county from Worcestershire, hit 17 boundaries in a total of 109 not out as Notts reached 324 for five at the close against Yorkshire at Trent Bridge.
Opener Ben Slater also performed well, hitting 76 before he was caught behind off the bowling of another debutant in South African Duanne Olivier.
Sam Northeast was closing in on a century for Hampshire against Essex when bad light brought an early end to play in Southampton.
Northeast hit 12 fours and one six in his 94 not out and was ably supported in a strong batting performance as Hants reached 303 for four.
Debutant Aiden Markram made 63 while Northeast put on 117 with Rilee Rossouw, who hit a quickfire 76 from only 66 balls.
There was no play in the other Division One clash between Somerset and promoted Kent because of rain.
Fifteen wickets fell on an eventful day in the Division Two match at Hove between Sussex and Leicestershire.
Tom Taylor produced a fine performance with the ball, taking six for 47 as Sussex were bowled out for 173. Three batsmen were snared for ducks, while David Wiese offered the most resistance with 51.
Leicestershire fared marginally better, ending the day on 131 for five. They were in big trouble at 59 for five but Harry Dearden and Lewis Hill put on an unbeaten partnership of 72.
Derbyshire rallied after a terrible start to reach 197 in their first innings against Durham at the County Ground.
Luis Reece and Wayne Madsen were both out for ducks in the first three balls, victims of Chris Rushworth, and at one stage the home side were 63 for five.
But Harvey Hosein led the revival with 78 before he was run out, and Durham also found the going hard with the bat, reaching 41 for three at the close.
Northamptonshire edged the first day against Middlesex at Wantage Road, amassing 310 for six.
Captain Alex Wakely top scored with 76 before he was one of four scalps for Tim Murtagh. Adam Rossington chipped in with 67 while West Indies captain Jason Holder was 36 not out at the close on his debut.