Swindon finished 5th in League One and faced Charlton. After winning 2-1 in the first leg, they were on the end of a 2-1 defeat, eventually taking the game in to penalties.
Darby dispatched the last of the 5 Swindon penalties to spark jubilant scenes amongst the away supporters.
Huddersfield take on Millwall in their second leg tonight, with a place at Wembley on the 29th May at stake.