|NatWest T20 Blast, The BrightonandHoveJobs.com County Ground|
|Sussex 165-7 (20 overs): Nash 53, Jayawardene 50; Willey 3-27|
|Northants 166-3 (16 overs): Willey 100; Beer 2-24|
|Northants won by seven wickets|
David Willey took three wickets and smashed a century off 40 balls as Northants beat Sussex by seven wickets to reach T20 Blast Finals Day.
The England one-day all-rounder hit 34 off one Michael Yardy over as the 2013 winners reached their target of 166 with four overs to spare.
He brought up his century with one of his 10 sixes and also hit seven fours before falling to Tymal Mills.
Willey, 25, had earlier taken 3-27 as Sussex posted 165-7.
Sussex lost captain Luke Wright to a duck but former Sri Lanka batsman Mahela Jayawardene and Chris Nash both hit half-centuries to lay the platform for a potentially challenging total.
But once Jayawardene fell to a brilliant one-handed diving catch on the boundary by Josh Cobb the Sussex innings fell away.
|How Willey's innings compares|
|Willey's century was the joint-seventh fastest in T20 cricket||Willey's century was the third fastest in T20 cricket in England|
|Chris Gayle hit the format's fastest ton off 30 balls for Royal Challengers Bangalore v Pune Warriors in 2013||It is fastest this summer, beating Brendon McCullum's 42-ball ton for Birmingham v Derbyshire|
Willey signalled his intent to attack by lofting fit-again England all-rounder Chris Jordan's first ball since recovering from a side strain for six.
He had passed 40 by the time opening partner Richard Levi hit his first boundary and reached his half-century with a six off the first ball of Yardy's second over.
The second ball went for four before Willey dispatched the remaining four deliveries of the over high over the ropes and into the stands in an astonishing display of hitting.
He reached his maiden T20 century with another six before being caught by George Bailey off Mills from the very next ball.
By then Northants' place at Edgbaston on 29 August was already assured and it was left to captain Alex Wakely to hit the winning runs.