Swansea reached the first major cup final in their history as a goalless draw saw them beat Chelsea 2-0 on aggregate - but the achievement was overshadowed by a moment of madness from Eden Hazard.
With just over 10 minutes remaining of the Capital One Cup semi-final second leg, and Chelsea needing to score twice to take the tie to extra-time, the Belgian lost patience when a ball boy refused to hand over the ball after it had gone out of play for a goal-kick.
The ball boy fell to the ground as Hazard attempted to get the ball from him with the forward trying to kick it from under him but instead he appeared to make contact with the youngster.
Several Chelsea players went to tend to the ball boy, who was left holding his ribs, before referee Chris Foy produced a red card.
Demba Ba, who started in place of Fernando Torres, and Oscar failed to convert Chelsea's best chances, as Swansea showed the same resilience that characterised their first-leg win at Stamford Bridge to book a Wembley appointment with Bradford.
Benitez had opted for Ba up front with his side needing goals, and Fernando Torres not having found the net since 23 December.
The Chelsea manager had predicted Swansea would look to sit back and protect their two-goal advantage from the first leg, but the hosts instead took Michael Laudrup's advice to be bold during a sharp opening.
They first had to survive a penalty scare after Ba went down under a challenge from Ben Davies.
Foy opted not to point to the spot although there was contact as Ba looked to step inside the full-back.
While Chelsea complained Swansea broke sharply and it took a superb block from Cesar Azpilicueta to keep out Wayne Routledge's fierce goalbound volley.
Michu, fresh from signing a new four-year contract, was the next to test the Chelsea rearguard from Routledge's reverse pass, but found Petr Cech equal to his angled drive.
Jonathan de Guzman also had a volley blocked, this time by Gary Cahill, as the hosts sought an early goal to take the tie further away from the European champions.
But Chelsea began to assert an authority on proceedings having weathered that flurry, and Swansea dropped progressively deeper as the half wore on.
It took 31 minutes for the Blues to genuinely threaten the Swansea goal, and when they did Oscar failed to take a great chance as Ashley Williams nipped in after a ricochet fell to the Brazilian in the box.
Angel Rangel cleared Gary Cahill's looping header off the line as the pressure increased, while Ba wasted another opportunity late in the half as he scooped a shot over the bar after Davies and Routledge had got in each other's way clearing a corner.
The former Newcastle striker was again off-target with a curling strike from the edge of the area five minutes into the second half, but Laudrup was by now imploring his defenders to get out of their own 18-yard box.
Frank Lampard and Juan Mata linked beautifully on the right, moments after taking part in an awful free-kick routine, but yet again there was a white shirt in the way to block the Spaniard's attempted ball across the six-yard box.
Gerhard Tremmel made a sharp stop to deny a fizzing effort from Hazard as the game entered the final 20 minutes, and Chelsea's hopes were effectively ended when Hazard was then dismissed in unsavoury fashion.
Pablo Hernandez and Nathan Dyer missed chances to secure victory on the night as Cech saved on both occasions, with the stadium still stunned by Hazard's astonishing dismissal.
And Swansea comfortably saw out six minutes of stoppage time to reach Wembley.