The odds may be stacked against Bayern Munich and Paris Saint-Germain heading into the second leg of their respective Champions League quarter-final ties, but history suggests that there is still plenty of hope of progressing.
Pep Guardiola's men were stunned by Porto last week, falling to a 3-1 defeat - a deficit the German club have never successfully overturned - while PSG were outclassed by an impressive Barcelona side to lose by the same scoreline in the French capital.
Over the years, many sides have found themselves in similar positions and, while many have ultimately exited the competition having found the task simply too hard to overcome, many more have bounced back in style.
Here, Sports Mole picks out five of the European Cup's greatest second-leg turnarounds.
AS Monaco 5-5 Real Madrid (2003-04, quarter-finals)
This two-legged affair started well and certainly ended well for AS Monaco, it is just a shame about what took place in between. Sebastien Squillaci bundled home the opening goal of the tie following some shaky defending from the Spanish giants, but four second-half goals from the hosts at the Bernabeu seemed to have all but sealed Monaco's feat.
Incredibly, it was Fernando Morientes, on a season-long loan at the Red and Whites from Madrid, who pulled back a late consolation to set up an intriguing follow-up meeting. Progression looked as far away as ever when, with seconds to go before half time in the rematch, Didier Deschamps' men fell further behind. Then came something special as Ludovic Giuly's double, plus another from Morientes, pulled off the most unlikely of results as Monaco took their place in the final four thanks to the away goals rule.
Chelsea 5-4 Napoli (2011-12, round of 16)
A memorable European season for Chelsea, which saw them go all the way and lift the trophy in Bavaria, very nearly came to an abrupt end at the round-of-16 stage. The impressive victories over Barcelona and Bayern no doubt stand out, but it was this turnaround in the early part of the knockout round which paved the way for those memorable nights further down the line.
Trailing 3-1 from the first leg, a result which, coupled with a 1-0 defeat against West Bromwich Albion just a few days later, cost Andre Villas-Boas his job, saw Roberto Di Matteo placed in temporary charge. What a decision that turned out to be, as goals from Didier Drogba, John Terry and Frank Lampard helped pull off what the Italian boss would later describe as one of the greatest nights in the West London outfit's history.
Manchester United 5-6 Real Madrid (2002-03, quarter-finals)
A year before their collapse in the south of France, Madrid did something similar in their quarter-final meeting against Manchester United. This was always likely to be a match which would remain in the memory, as two of the best sides on the continent came face-to-face. Heading into the game looking to overturn a two-goal reverse from the first leg, United, minus David Beckham who was watching on from the bench, had come so close to pulling off a huge upset if not for the brilliance of Ronaldo.
Ruud van Nistelrooy had cancelled out the Brazilian's earlier effort, but the three-time World Player of the Year - who left the pitch to a standing ovation - struck twice more early in the second half. Beckham, a future Madrid player, came off the bench to score a brace which pulled his side right back into the game, although there was to be no Champions League final appearance on home soil as Vicente del Bosque's charges held on to continue their European march.
Deportivo La Coruna 5-4 AC Milan (2003-04, quarter-finals)
While it was a case of so near yet so far for United, Deportivo successfully got the job done as they trounced a star-studded Milan side to book their place in the semi-finals. Strikes from Andriy Shevchenko and Andrea Pirlo, coupled with Kaka's well-taken double, helped the Italian giants end the opening 90 minutes on top following an eight-minute siege in front of goal.
It took just 45 minutes of the second leg for La Coruna to level things up overall, however, as Walter Pandiani - a scorer in the first leg - Juan Carlos Valeron and Alberto Luque made it 3-0 on the night. It was then left to substitute Fran Gonzalez to complete arguably the most impressive salvo in the competition's history, as he found the tie's ninth goal on 75 minutes to send Milan packing.
Barcelona 4-2 AC Milan (2012-13, round of 16)
On the face of it, this may not seem like a truly memorable comeback, but it marked the first time in the elite tournament's history that a side had bounced back from a two-goal first-leg defeat and progressed through without the aid of an away goal. An on-song Lionel Messi helped put Barca on their way with two fine goals in the opening throes of the reverse meeting, leaving things delicately poised.
David Villa put the La Liga club ahead for the first time early in the second period, but the contest was not sealed until Jordi Alba burst through on goal to wrap up the round-of-16 win late on. Barcelona would go on to beat PSG of all sides at the quarter-final stage, before being crushed 7-0 on aggregate by a rampant Bayern Munich in the following round.
