The Blues came up with a 2-2 draw against the odds to go through to the May 19 decider 3-2 on aggregate following the 1-0 win at Stamford Bridge last Wednesday.
It was a huge night of drama in Spain which saw Barcelona take a two-goal lead as Chelsea skipper John Terry was sent off prior to half-time before Lionel Messi missed a penalty and then substitute Fernando Torres scored late to wrap up the win.
Roberto Di Matteo's men had come to try and defend their lead and it was a fairly slow beginning to the match before it sprung into life in the 35th minute when Sergio Busquets opened the scoring for Pep Guardiola's Barca, finishing easily for his second goal in two years after Isaac Cuenca had found space down the left and crossed it low to the edge of the six-yard box.
Two minutes later, Terry was given his marching orders for an inexplicable act when he kneed Alexis Sanchez in the back in an off-the-ball incident which could only be described as a brain fade. The loss of a second centre-back, after Gary Cahill had to come off with a hamstring injury, was quick to put the Blues a further goal behind on the night when Messi played in Andres Iniesta with the Spanish midfielder slotting past Petr Cech in the 43rd minute.
But just as it seemed like it was curtains for Chelsea, Ramires produced a deft chip over an advancing Victor Valdes after Frank Lampard had found him with a divine through ball to put the West Londoners ahead on away goals at half-time.
Barcelona came out firing in the second term with their customary domination of possession and attempts on goal and they should have gone ahead in the 48th minute after Didier Drogba had brought down Cesc Fabregas in the area. However, Messi stepped up to put his spot-kick onto the crossbar in what was a huge letoff for the visitors.
From there it was a matter of defence at all costs for the Blues who repelled wave after wave of Barcelona attack with Cech denying Cuenca from an angle in the 62nd minute before getting a vital finger tip onto Messi's effort from just outside the area.
It was all set up for a grandstand finish and it did come but it was the Blues who produced it with Torres latching onto a long clearance from Ashley Cole before advancing into the area, rounding Valdes and slotting it into the back of the net for his eighth goal in 11 matches against Barca to wrap up a famous triumph for Chelsea.
Di Matteo's men will now await the winner of the Real Madrid v Bayern Munich tie tomorrow night but will be without Terry for the final as well as Raul Meireles, Branislav Ivanovic and Ramires who all received bookings tonight. Nevertheless, they are through to the decider for the first time since they lost to Manchester United on penalties in 2008 and will go in with the belief that they can do a job no matter who they meet in Munich next month.
UEFA Champions League semi-final - second leg
Nou Camp, Barcelona
Red card:CHE - John Terry 37'