Central Group leaders Gloucestershire battered Birmingham Bears by 50 runs in Bristol to qualify for the T20 Blast quarter-finals.
That left them four points clear of both the Bears and Northants, who were beaten at home by Worcestershire.
But, as the Bears host Northants in the final game, Gloucestershire are guaranteed to finish in the top two.
In North Group, a surprise loss for Leicestershire, in third, by Derbyshire leaves Notts and Lancashire clear.
While Gloucestershire’s sixth straight win earlier in the day was no surprise, as they qualified for the knockout stage for the fourth time in five years, Northants’ shock third straight defeat leaves them now needing at least one win from their two remaining games at Taunton and Edgbaston to stand a chance.
Worcestershire, champions in 2018 and finalists again last season, already knew they could not qualify, but they finally found some form to claim only a second win.
Hamish Rutherford’s first half-century of the tournament – 62 in 37 balls – underpinned Worcestershire’s 178-6 before another fine Pat Brown last over ensured that Northants, 82-2 after eight overs, pulled up short on 170-7 to lose by eight runs.
Cockbain uncorks his finest again
Gloucestershire’s earlier win was inspired by Ian Cockbain, who followed his 84 not out in his side’s first group win over the Bears at Edgbaston 13 days before with a further 44 off 21 balls.
After Chris Dent (39) and Miles Hammond (49) had led the way with an opening stand of 88, that helped Gloucestershire total 173-6 – and the Bears did not even get close, being bowled out for just 123.
Only Sam Hain offered much resistance, still there at the end on 43 after spinners Matt Taylor (3-29) and Graeme van Buuren (3-33) had done the damage.
“To win six on the bounce is a great effort by the lads,” said Cockbain. “What we want now is to earn a home quarter-final because we know the conditions here and play them well.
“It’s just one of those things that I have been able to score big twice against the Bears. Sometimes you just feel it is your day and I’ve hit the ball sweetly in both games. But I probably got out to my sweetest hit of the lot.”
Derbyshire claim first win
In the other evening game, in North Group, third-placed Leicestershire’s hopes were dented by Derbyshire’s first win.
Having restricted the Falcons to 147-8, seamer Gavin Griffiths taking a career-best 4-35, the Foxes fancied their chances of cementing their position as one of the two best third-placed sides, especially after the Central Group defeat by the Bears earlier in the day.
But, despite an unbroken stand of 68 for the fifth wicket between Harry Dearden and George Rhodes, building on a useful 32 on home debut from Nick Welch, the Foxes fell short.
Tight and intelligent death bowling from Dustin Melton and Michael Cohen pinned them down over the final three overs, when neither batsman could find the boundary.
Wednesday, 16 September (start times BST)
14:00 – Hampshire v Essex Eagles – Ageas Bowl
14:00 – Kent Spitfires v Middlesex – Canterbury
18:30 – Glamorgan v Somerset – Cardiff
18:30 – Yorkshire Vikings v Durham – Emerald Headingley
18:30 – Surrey v Sussex Sharks – Kia Oval