Glamorgan secured their place in the Yorkshire Bank 40 final with a 31-run victory over defending champions Hampshire in Southampton.
Jim Allenby impressed with bat and ball for the Welsh county, hitting 74 not out in a total of 234-4 and then taking 2-18 as Hampshire's run chase finished short on 203-8.
Glamorgan's win was their first over Hampshire in any form of limited-overs cricket since 2005 and means they are into a Lord's final for the third time in their history - and first in 13 years.
Allenby's 71-ball contribution built on the steady start provided by Glamorgan's top three after they had been sent in to bat.
Mark Wallace (18) and Gareth Rees (25) shared an opening stand of 30 before falling to Hampshire seamers Sohail Tanvir (2-40) and Chris Wood (1-58) respectively.
Chris Cooke contributed 37 but his departure, lbw to Danny Briggs' left-arm spin, left Glamorgan on 99-3 in the 21st over.
Allenby took control of the remainder of the innings, putting on 51 with Murray Goodwin (27) and an unbroken 84 alongside Ben Wright, whose 28-ball 47 not out provided a late flourish.
Hampshire openers James Vince (20) and Michael Roberts (23) both fell to Allenby's medium pace and Neil McKenzie (7) was run out to leave Hampshire on 73-3 in the 19th over.
Despite half-centuries from Jimmy Adams (59) and Sean Ervine (54), the required-rate began to spiral.
The return of seamer Michael Hogan (4-51) for his second spell turned the game decisively in Glamorgan's favour.
The Australian, who is the leading wicket taker in the tournament and recently signed a new deal to remain in Cardiff, accounted for Adams, Ervine, Liam Dawson (17) and Wood (3) as Hampshire's cup defence petered out.
Former England all-rounder Dimitri Mascarenhas, in the final game of his 17-year Hampshire career, finished on eight not out after earlier going wicketless.
Glamorgan await the winner of Monday's second semi-final between Nottinghamshire and Somerset at Trent Bridge.
The final takes place at Lord's on September 21.