Glamorgan Dragons defeated reigning champions Hampshire Royals by 31 runs at the Ageas Bowl on Saturday to reach the YB40 final.
After being put to bat by the home side, the Welsh outfit posted a score of 234-4, with all of their batsmen reaching double figures.
The contest then swung further Glamorgan's way when Mark Wallace ran out former South African international Neil McKenzie, although a 77-run partnership between Jimmy Adams and Sean Ervine put Hampshire back on track.
Both batsmen would make half-centuries before they fell victim to Michael Hogan's match-winning spell, which helped him record figures of 4-51 from eight overs.
The Royals lower order struggled and they continued to fall behind the run-rate and Hampshire eventually finished on 203-8, allowing Glamorgan to qualify for their first Lord's final in 13 years.
The Dragons will face the winner of Nottinghamshire Outlaws and Somerset Sabres, who meet in the competition's other semi-final on Monday.