Striker Darryl Duffy booked Swansea City a place in the Johnstone's Paint Trophy southern area final at the Liberty Stadium.
Duffy's first-half header was good enough to earn the Swans victory over a battling Brighton side and move them to within two-legs of a dream date at Wembley.
The Swans will now play League Two leaders MK Dons in the area final after Willy Gueret's side beat Gillingam 5-4 on penalties in the other semi-final which ended all square 1-1 at the end of 90 minutes.
Swansea City:
de Vries, Rangel, Painter, Monk (c), Lawrence, Anderson, O'Leary, Allen, Orlandi, Duffy, Bauza. Subs: Britton, Pratley, Scotland, Butler, Knight.Brighton: Kuipers, Lynch, El-Abd, Cox, Revell, Forster (c), Fraser, Loft, Elphick, Fogden, Martot. Subs: Mayo, Hart, Sullivan, Rents, Elder.
Ref: J Singh
Asst-refs: A J Horton, B J Malone
4th official: D C Richards
Att: 6,066 Away: 110
Swans boss Roberto Martinez made wholesale changes for this southern area semi-final with Kristian O'Leary, Andrea Orlandi, Darryl Duffy, Dennis Lawrence, Garry Monk, Angel Rangel, Guillem Bauza and Paul Anderson the changes from the side that drew with Havant & Waterlooville in the FA Cup on Saturday.
They faced a Brighton squad that had been struggling with a bug in the week.
Wes Fogden, 20, came in foe his debut, while Gary Hart made the bench after being recalled early from a loan spell at Havant.
As the rain poured down at the Liberty, it took Swansea nine minutes to make the breakthrough.
Angel Rangel made his usual probing run down the right and when his cross took a deflection off the head of a Brighton defender, Darryl Duffy was perfectly placed to head home.
Swansea were full of confidence now and nearly increased their lead in the 14th minute. Marcos Painter combined well with Andrea Orlandi down the left before Painter drove a fierce cross across the face of goal. Guillem Bauza arrived late, but his touch just flew wide of the far post.
Nicky Forster beat the offside trap at the other end to create Brighton's first chance which Swansea cleared, before Bauza set Duffy racing in on goal with 21 minutes gone. But goalkeeper Michael Kuipers did well to save his low shot with an outstretched leg.
Swansea remained in control, although they had a scare in the 28th minute when Dean Cox turned Garry Monk on the edge of the area. But the striker fired straight at Dorus de Vries.
Half-time: Swans 1 Brighton 0
It was Brighton who created the first opening of the second half when Cox split the Swansea defence with a through ball. Forster was in the clear just inside the area, but de Vries pulled off a great save.
Swansea were struggling to keep hold of possession early on as Brighton enjoyed a good spell as the hour mark arrived.
The closest the visitors came though was a 20 yard shot from Doug Loft which flew well over the bar, before Brighton were forced into their first substitution with Sam Rents replacing the injured Joel Lynch with 65 minutes gone.
Tom Butler came on for Swansea at the same time for Paul Anderson.
Brighton remained on top though as Swansea kept given the ball away in uncharacteristic fashion.
Orlandi did force Kuipers into a save with 72 minutes after cutting in from the right, before Leon Britton came off the substitutes bench in place of Joe Allen in a bid to regain control and make the game safe.
Six minutes later and Darren Pratley was also on as Swansea's last substitute; replacing the goalscorer Darryl Duffy.
Pratley nearly found himself on the conceding end in the 80th minute though as a long ball from Adam El-Abd caught the Swansea defence square. Brighton's best player Dean Cox sprinted in behind, but again de Vries pulled off a great save.
Pratley was quick o get himself into the game, however, as his shot took a deflection off David Martot and was creeping into the bottom corner until Kuiper pulled off a good reaction save.
