Sent into bat, Lancashire made 166 for seven in their 20 overs, a total built on a 77-run opening stand between South Africa’s Ashwell Prince (43) and Alex Davies (47), who was named man-of-the-match.
Afridi, Pakistan’s T20 captain, helped check Lancashire’s progress, the veteran all-rounder taking a superb three for 14 in a maximum four overs with his leg-spinners.
Meanwhile, Northampton-born David Willey, set to leave his native side for county champions Yorkshire, saw his left-arm fast-medium bowling yield figures of two for 21.
Northamptonshire had stormed into finals day on the back of Willey’s blistering 40-ball hundred against Sussex — the quickest Twenty20 century by an Englishman.
The way he struck Australia’s James Faulkner into the Eric Hollies Stand for six on Saturday hinted at similar fireworks in the final.
But Faulkner responded by removing Levi (16) and England limited overs all-rounder Willey (24) in the space of four balls, with the aid of catches at mid-off and mid-wicket respectively.
Josh Cobb (44 not out) and Afridi (26) revived Northamptonshire’s hopes with a rapid fifth-wicket stand of 52.
‘Boom Boom’ struck one huge six while another fierce hit straight back at Faulkner left the Australian needing to have his finger straightened out by a member of the Lancashire medical staff.
But Gavin Griffiths effectively ended Northamptonshire’s victory charge when he induced Afridi to hole out to Liam Livingstone in the deep.
The semi-finals saw Lancashire dismiss Hampshire for 115 in a six-wicket win, while Northamptonshire beat Edgbaston-based Warwickshire by five wickets, with Levi making 63 not out as they chased down a target of 132.