To say that Real Madrid and Barcelona face uphill battles in their Champions League semi-final second legs this week would be something of an understatement.
In fact, the only people who'll have a tougher uphill battle this week are the three British climbers who were set upon by a mob of furious Sherpas while they were climbing Mount Everest a few days ago.
Bookies don't give them much hope: Real are, appropriately, 4-1 to overturn their 4-1 deficit on Tuesday and make the final, while Barcelona are 20-1 to undo the damage from their 4-0 first leg defeat at the hands of Bayern Munich when they play the German champions on Wednesday.
Can they do it? Well, stranger things have happened - and if any two players in the world can inspire the sort of mutiple-goal thrashings needed, it's Lionel Messi and Cristiano Ronaldo.
You'd have to be made of stone - or a die-heard Bayern or Dortmund fan - not to hope that one or both of the Spanish sides at least make a game of it. So in the spirit of inspiration, and to get you in the mood for some plucky underdog action, here's our pick of sport's most amazing comeback stories.
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Henri Cochet v Bill Tilden, 1927 Wimbledon semi-final
France's Cochet was given little hope of winning as he took on American star Tilden in the men's singles semi-final in 1920. Tilden was regarded at the time as the greatest player ever to swing a racquet, and it was no surprise when he romped through the opening two sets and took a 5-1 lead in the third.
Cochet, thoroughly beaten, started going for anything and everything - but something miraculous happened as he suddenly started finding all the lines. He won six games in a row to win the third set 7-5, then won the final two sets 6-4 6-3. Almost as incredibly, Cochet had also recovered from two sets down in the quarter-final, and would do so again as he beat compatriot Jean Borotra in the final.
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Sugar Ray Leonard v Thomas Hearns, world welterweight title fight 1981
WBC champion Leonard faced the undefeated WBA title-holder Hearns at Caesar's Palace in one of the greatest fights in boxing history. Hearns was miles clear on the scorecards as early as the sixth round, while Leonard had a swollen eye, and despite a wobble in the seventh and eighth rounds it looked as if Hearns would cruise to victory.
Then came the now-legendary words of Leonard's trainer, Angelo Dundee, after the 12th round: "You're blowing it, son! You're blowing it!" Leonard unleashed everything at Hearns, knocking him down twice in the 13th, and then pummelling him so badly on the ropes in the next round that the referee stepped in to declare him the winner.
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John Watson wins the 1983 US Grand Prix from 22nd on the grid
McLaren driver Watson and his team-mate Niki Lauda had both struggled appallingly in qualifying, struggling to get the balance of the car right and starting from the back of the grid at Long Beach, California. But they finally cracked the set-up in final practice, and after a series collisions ahead of them (only half the 26-car field finished the race) Watson and Lauda climbed up to third and fourth respectively just a third of the way into the race, albeit 20 seconds off leaders Jacques Laffite and Riccardo Patrese. Laffite's tyres were deteriorating badly, however, and Patrese ran wide as he tried to overtake, letting the McLarens through to complete perhaps the most incredible 1-2 ever seen in F1.
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Liverpool v AC Milan, 2005 Champions League final
Just over twelve months before the 2005 final, the Champions League witnessed its greatest ever comeback when Deportivo La Coruna turned a 4-1 first leg deficit into a 5-4 win over AC Milan in the quarter-finals. But Milan appeared to have laid that ghost to rest in style as the Italian giants tore Liverpool to shreds in a stunning opening half in Istanbul, carving out a 3-0 lead.
Rafael Benitez's men looked dead and buried: coming back from three goals down in 90 minutes in a quarter-final second leg is one thing, but with just 45 minutes left in the final? Surely it was impossible.
Skipper Steven Gerrard had different ideas, however, inspiring an incredible spell of play that saw the Reds score three goals in six minutes to force extra time. The game went to penalties, and Liverpool won as Jerzy Dudek saved from Andriy Shevchenko to complete the match now known as 'The Miracle of Istanbul'.
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Stephen Hendry v Jimmy White, 1992 snooker World Championship final
White will forever be referred to as the "People's Champion", but never landed the one tournament he wanted to win the most: the World Championship. The 1992 final looked certain to see him break his duck as he roared into a 14-8 lead.
Hendry, with nothing to lose, simply started throwing everything at his opponent, potting an astonishing brown to avoid going 15-9 down two frames later. He returned for the evening session with a bang, immediately clinching a key black ball frame, then banging in break after break - including three centuries -reeling off 10 straight frames to win 18-14.
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Boston Red Sox v New York Yankees, American League Championship Series 2004
The Red Sox looked on course to be humiliated by their greatest rivals as they lost the first three games of the best-of-seven series, and trailing by a run in the ninth inning of game four it looked like it was all over for another year.
But an amazing stolen base by Dave Roberts - one of the most famous in baseball history - helped him score a tying run. David Ortiz then smashed a home run for the Red Sox in extra innings to win the game, and the Boston side won the next three games in a row (thanks to another Ortiz home-run in extra innings) to make it to the World Series, where they went on to beat the St Louis Cardinals 4-0.
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England v Australia, 1981 Ashes Test at Headingley
After Australia scored 401 in the first innings of the third Test, they seemed certain to go 2-0 up in the series after bowling England out for 174 in the second innings and enforcing the follow-on. England then lost an early wicket in their second innings to go in on the third day at 6-1.
They were 500-1 to win the Test at that point, a price so great that Australian stars Rodney Marsh and Dennis Lillee decided to pop a few quid on just in case. It was a decision which would later prove highly controversial, but didn't look like being so as England were reduced to 105-5, and then 135-7 at tea on the fourth day.
Then, however, it all changed as Ian Botham started swinging at everything, getting to 145 not out and putting England into a lead of 124 at stumps - and prompting England to find a new hotel, having checked out of theirs that morning assuming that they were about to lose. England added just four more runs in the morning, but Bob Willis's bowling on the final day was equally as heroic as Botham's batting had been as he took 8-43, England winning by 18 runs. The inspired team then went on to win the Ashes.
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The European Ryder Cup team v USA, 2012
Europe's performance in the Ryder Cup match in Medinah last September was, for two days, abject. Only some outrageous brilliance from Ian Poulter in the foursomes and fourballs kept the visitors even vaguely in the picture, but they still went in to Sunday's final day needing the greatest ever singles performance ever seen on foreign soil if they were to avoid losing the trophy. Several US papers openly declared that the match was over.
Skipper Jose Maria Olazabal's plan was simple: put out his best players first, get the scoreboard turning blue, and hope that momentum would carry everyone along. It was a good idea, but the plan was faltering as Justin Rose was on the verge of defeat by Phil Mickelson on the 16th hole. But Rose over the next three holes the Englishman rolled in the best three putts of his life - including a 50-footer from off the green on the 17th - and the tide turned blue, for good. The visitors had been 10-4 down at one stage, but won the Ryder Cup 14.5 points to 13.5.
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South Africa v Australia, one-day international 2006
The tourists batted first in the ODI in Johannesburg, and looked to be on course for a crushing victory as Ricky Ponting's 164 from 105 balls saw them record 434-4 from their 50 overs, the highest score ever seen in a one-day innings.
South Africa looked certain to capitulate when opener Hendrik Dippenaar was bowled for a single run, but Graeme Smith and Herschelle Gibbs then took the fight to the Aussies. Smith's 90 from 56 balls and Gibbs's 175 from 111 still left South Africa 135 runs short of their target, but the rest of the side all chipped in until Mark Boucher nailed the penultimate ball for four to win the match as South Africa made it to 438-9.