Hampshire were favourites to secure promotion, but Kent's resistance and an Essex win have complicated matters.
All-rounder Will Smith has signed a new two-year contract extension to remain at Hampshire.
Jesse Ryder claimed career-best first-class bowling figures to keep Essex in contention for promotion in Division Two.
Jos Buttler has been reprimanded for dissent by the England and Wales Cricket Board's disciplinary committee.
Matt Coles and Sean Ervine each took three cheap wickets as Hampshire crushed Leicestershire by an innings and 34 runs.
Worcestershire's clash against Derbyshire at Derby is firmly in the balance heading into the final day of play.
Derbyshire made life difficult for Division Two leaders Worcestershire on day two, while rain frustrated Hampshire.
Hampshire have signed seamer Andre Adams on a short-term deal for the first three months of next season.
Derbyshire's batsmen held up Division Two leaders Worcestershire, while Angus Robson and Chris Cooke hit maiden tons.
Lancashire beat Hampshire by 41 runs (D/L) in a rain-affected second NatWest T20 Blast semi-final at Edgbaston.
Kevin Pietersen and Andrew Flintoff could both feature at Finals Day after the squads were unveiled on Friday.
Derbyshire's home victory over Gloucestershire saw them qualify for the quarter-finals of the Royal London One-Day Cup.
Vote for your favourite catch in the NatWest T20 Blast so far from our spectacular short-list of five.
We take a look back at some of the highlights from previous Finals Days ahead of this year's event.
South Africa spinner Imran Tahir is set to return to Hampshire for the final two games of the County season.
We look at the form and men to watch from the four teams vying for Twenty20 glory on Finals Day.
A brilliant innings by Richard Oliver failed to prevent Worcestershire's first Championship defeat of the season.
Hampshire have secured the future of left-arm seamer Chris Wood on an extended deal to the end of the 2016 season.
Essex opener Tom Westley and Ryan ten Doeschate plundered centuries to help their side beat Yorkshire by five wickets.
Yorkshire Vikings took control of Group A in the Royal London Cup with a three-wicket victory over Leicestershire Foxes.
Hampshire wicketkeeper Adam Wheater has been suspended for two matches under the ECB's disciplinary code.
Niall O'Brien's ton helped Leicestershire beat Hampshire by six wickets in a rain-hit Royal London One-Day Cup clash.
Hampshire skipper James Vince revels in 'special' T20 Blast quarter-final win for his side over Nottinghamshire.
James Vince scored an unbeaten 93 as Hampshire overhauled Nottinghamshire's 197-2 to reach NatWest T20 Blast Finals Day.
Hampshire will play Lancashire in the NatWest T20 Blast semi-finals, while Surrey will take on Birmingham.