Ollie Robinson pressed his England claims with a match haul of 8-65 as Sussex overcame Hampshire to become the first side to win a match in the inaugural Bob Willis Trophy.
Robinson, called up for England's training squad after impressing for the Lions last winter, took 5-29 to bowl out Hampshire for 153 and seal Sussex's win by 94 runs.
Skipper Ben Brown was pleased with both Robinson and opener Phil Salt, another of Sussex's recent England squad members, who hit 68 and 80 in a low-scoring match - well over a third of his side's total runs.
"Ollie Robinson's performance was the sort we've come to expect," said Brown. "He's in really good rhythm. The spell of three wickets in 14 balls before lunch made such a difference.
"Phil Salt batted well in both innings. He was in good form for England with that hundred in the warm-up game against Ireland. He's an attacking player but I don't think people realise what good defensive technique he has, which you need if you open the batting in England."
Elsewhere on day three of the delayed, severely truncated county season, several matches are heading towards an exciting climax, including at Chelmsford where it seems like normal service has been resumed.
Essex, the 2017 and 2019 county champions, turned their match around by bowling out Kent for 112 - and last year's leading wicket-taker Simon Harmer claimed four of them.
Yorkshire need another 68 to beat Durham at Chester-le-Street with seven wickets in hand going into the final day, despite Tykes old boy Alex Lees' first century against his old county.
Lees made 106 before becoming one of fast bowler Matt Fisher's four wickets in six overs.
After losing their last seven wickets for 45 to be bowled out for 266, that set Yorkshire 171 to win.
And although Chris Rushworth made early inroads, claiming Tom Kohler-Cadmore as his 500th first-class wicket, new signing Dawid Malan survived a dropped chance to reach an unbeaten 50 as Yorkshire closed on 103-3.
Derbyshire made a bright start chasing 365 to win against Nottinghamshire.
Samit Patel hit 80, his second half-century of the match, to help Notts post 279, but Billy Godleman (69*) and Wayne Madsen (27*) steered Derbyshire to 129-1 at the close, reducing that target to 236.
Meanwhile, Notts batsman Ben Slater remained in the runs on his loan debut for Leicestershire in the unlikely setting of Worcester - forced into emergency use as the city of Leicester is in lockdown and Old Trafford is being used by England.
Slater went on to make a career-best 172, supported by Colin Ackermann's 94, as the Foxes declared on 409-8 against a weakened Lancashire attack containing three debutants, before the 'hosts' closed on 96-3, only nine runs in front.
Any hopes Warwickshire had of triggering a three-day finish against Northamptonshire were hit first by a side strain to their main spearhead, luckless England fast bowler Olly Stone, then by a 159-run stand between Charlie Thurston (96) and Adam Rossington (60*), their county's best for the sixth wicket at Edgbaston since 1939.
Trailing by 227 on first innings, the visitors closed on 317-6, 90 ahead, but after the perhaps crucial late loss of Thurston, who fell lbw to Tim Bresnan, making him the ex-Yorkshire and England all-rounder's third victim.
Gloucestershire remain in arrears to Worcestershire at Bristol on 135-3, after the late loss of Chris Dent for 67, his second half century of the match.
Following his four first-innings wickets, Charlie Morris struck a potentially crucial blow by removing Dent, to leave the hosts still 26 behind with only seven wickets left.
Somerset skipper Tom Abell made his sixth first-class century to set up an expected win against Glamorgan.
Abell resumed on 44 and was finally dismissed for 119, aided by 54 from Ben Green, a concussion replacement for George Bartlett.
After Somerset declared on 290-8, setting Glamorgan 456 to win, the visitors slumped to 29-3 before Chris Cooke's unbeaten 67 helped the Welsh county close on 126-5, still needing another 330.
Essex made a poor start to the new campaign on day one when a Heino Kuhn-inspired Kent helped his side pile up 387 at Chelmsford - but the hosts have battled back well.
Home skipper Ryan ten Doeschate's 78 helped Essex reach 298, to trail by only 89 before Harmer (4-35), Sam Cook (3-19) and Jamie Porter (2-31) bowled out Kent cheaply.
That set Essex 202 to win and, after nightwatchman Porter survived one over from Matt Milnes, they now have all day to get them - with Sir Alastair Cook next man in.
At The Oval, Middlesex have taken full control of the London derby after Surrey old boy Tim Murtagh's devastating second-new-ball spell of 6-5-4-4.
In the space of 15 overs either side of lunch, Surrey lost their last seven first innings wickets for just 28. And Middlesex then reached 184-3 to stretch their overall lead to 249.
Nick Gubbins followed up his first innings 192 with 49 not out, while Max Holden made 43 and Martin Andersson is still there on 35 off just 37 balls.
Sussex have set the benchmark with the 19 points they claimed for their win over Hampshire. But their lack of any batting bonus points means that they will be overtaken at the top if either of the other two South Group games reach a positive conclusion.