Chelsea’s backs-to-the-wall display against Barcelona in Camp Nou is their greatest achievement in Europe.Even if they go on to win the Champions League this year, Tuesday night will be remembered as the moment the impossible, suddenly became possible.It was a performance that might have superseded Manchester United’s display on this very same pitch in 1999, when Sir Alex Ferguson’s side beat Bayern Munich in the final that year.Mario Basler’s early goal appeared to have won it for the Bundesliga giants. But, in the final stages as the game approached injury-time, Teddy Sheringham stabbed home to bring the Red Devils level.Seconds later, David Beckham’s corner was headed on to Ole Gunnar Solskjaer, who toe-poked into the roof of the net to complete a dramatic turnaround, and give United a late 2-1 victory.Arguably even more memorable, was Liverpool’s comeback against AC Milan in the 2005 final in Istanbul.Rafa Benitez’s men were 3-0 down at half-time and staring down the barrel of a disappointing defeat, before Steven Gerrard, Vladimir Smicer and Xabi Alonso drew the Reds level in a whirlwind seven-minute spell to take the game to penalties.Up stepped Jerzy Dudek - the hero of the shootout - who saved from Andrea Pirlo and Andriy Shevchenko to clinch a stunning 3-2 victory.However, the latest Spanish success story might even trump both occasions as the most extraordinary contest ever witnessed in this competition. A 2-2 draw in Barcelona’s back yard confirmed the ten-man Blues’ place in the 2011-12 Champions League final, with a 3-2 aggregate victory over the greatest domestic side to grace the modern game.Their reward? A match against a Bayern Munich side who will be afforded the advantage of playing at their home stadium, the Allianz Arena in Germany on May 19.Chelsea will likely go into the game as underdogs, just as they have at every stage of the Champions League this year, and still made it through, against the odds.Before a ball had even been kicked and despite their slender 1-0 advantage ascertained from a dogged performance at Stamford Bridge last week, Barcelona were expected to make fairly light work of Chelsea’s challenge. But, the players obviously forgot to read the script.It looked ominous for the visitors the moment they lost Gary Cahill to injury after only 12 minutes, forcing Di Matteo to deploy Jose Bosingwa on the flank and move Branislav Ivanovic to centre half.When Sergio Busquets met a neat cross from Isaac Cuenca to break the deadlock just minutes later, Chelsea looked like they were facing an uphill struggle. Moments after the goal their misery was further compounded when captain John Terry was sent off after mindlessly kneeing Alexis Sanchez in the back in an off-the-ball incident.The assistant referee saw the coming together, and the defender was given his marching orders, leaving the Blues’ defence even more depleted, and prompting the need for another reshuffle. Ramires dropped into right-back, and substitute Bosingwa moved across to form an unlikely central defensive partnership alongside Ivanovic.And, when Andres Iniesta dropped off the right shoulder of the unfamiliar Brazilian full-back, to collect a perfectly weighted pass from Lionel Messi and slot past Petr Cech to double Barcelona’s lead, Chelsea were at risk of complete capitulation.But, in another unlikely twist before half-time, Ramires briefly restored belief when he ran the length of the pitch to latch onto a Frank Lampard through-ball, before dispatching the sublimest of chips over the outrushing Victor Valdes to make the scoreline 2-1 at the break.As the teams returned after the interval - Chelsea, a man light and with no recognised centre-backs on the pitch - the impetus was still firmly with Barcelona.Two minutes into the second-half, Didier Drogba brought down Cesc Fabregas in the box to concede a penalty, referee Cuneyt Cakir invited Messi to put daylight between the two sides once again, from all of 12 yards.But, the pint-sized magician has endured a difficult history with Chelsea, having failed to score against them in any of their seven meetings. When his penalty crashed against the bar before bouncing out of play, it looked destined to be extended to eight.In the remaining 43 minutes, Sanchez had a goal chalked off for offside, and when Cech pushed an exquisite Messi strike onto his post, as Chelsea’s rearguard stood strong, the Premier League club’s progression looked to be something that was written in the stars.And, as Fernando Torres - brought on in place of the diligent Drogba in the closing stages - broke free to level the scores, rounding Valdes to tap into an empty net, the visitors’ elation was there for all to see.Chelsea’s second goal was irrelevant in the end, but it was a fitting finale to a memorable European night, and provided a brief respite for the much-maligned £50million striker.With so many players missing through suspension, thanks to UEFA’s questionable ‘three yellow card’ ruling, it’s going to be another uphill battle for Chelsea in this year’s Champions League final. But, maybe being underdogs in Munich will work for them.