The gap between Europes elite and the rest seems to widen by the year, but the Champions League has remained fertile ground for a good old upset.
From the group stage right up to the final, the competition has seen its fair share of shock results over the years.
Here, weve picked out the biggest of the lot, spanning almost two decades of Champions League history.
Ajax 0-1 Panathinaikos (1995/96 semi-final first leg)
Ajax came agonisingly close to retaining their Champions League crown in 1996, losing on penalties to Juventus in the final but they had to win their semi the hard way, after losing the first leg 1-0 at home to surprise package Panathinaikos.
Krzysztof Warzychas late goal clinched victory in Amsterdam, giving the Greek side real hope of reaching their first Champions League / European Cup final since 1971 (when, incidentally, they were beaten by Ajax) only for the holders to take the second leg 3-0.
Dynamo Kyiv 2-0 Real Madrid (1998/99 quarter-final second leg)
Having been crowned European champions for the first time in 32 years the previous season, Real Madrid must have been confident of going all the way again in 1998/99. Dynamo Kyiv had other ideas
Coached by the legendary Valeriy Lobanovskyi, the Ukrainians were in a strong position after drawing the first leg of their quarter-final clash at the Bernabeu 1-1 thanks to a goal from a young Andriy Shevchenko who was at it again in the second leg, bagging a brace to send Dynamo into the last four.
Monaco 3-1 Real Madrid (2003/04 quarter-final second leg)
Porto winning the whole thing was an upset in itself, but the biggest one-off upsets in the 2003/04 Champions League came at the quarter-final stage, beginning with Monacos elimination of Real Madrid.
Los Blancos held a 4-2 lead going into the second leg in Monaco and extended that to 5-2 through Rauls opener, but Les Rouge et Blanc didnt cave, scoring three goals themselves two by Ludovic Giuly and one by Fernando Morientes (who was on loan from Madrid at the time!) to advance on away goals.
Deportivo La Coruna 4-0 Milan (2003/04 quarter-final second leg)
Another extraordinary comeback in the last eight of the 2003/04 Champions League saw Deportivo La Coruna overcome a 4-1 first-leg deficit against Milan the reigning champions, no less.
Walter Pandiani, Juan Carlos Valeron, Albert Luque (who made it 4-4 on aggregate and had his side ahead on away goals) and Fran were on the scoresheet as Depor who had knocked out another Italian giant, Juventus, in the previous round reached the semi-finals of the competition for the first time in their history.
Liverpool 3-3 Milan Liverpool won 3-2 on penalties (2004/05 final)
No neutral expected Liverpool to win the 2005 Champions League final the Reds had just finished fifth in the Premier League, almost 40 points off top spot and when Rafael Benitezs side trailed Serie A high-flyers Milan 3-0 at half-time, such expectations looked certain to be met in Istanbul.
Then surely the most incredible recovery in the history of the competition occurred: captain Steven Gerrard, Vladimir Smicer and Xabi Alonso had Liverpool on terms by just after the hour mark before Jerzy Dudek made himself the hero on penalties, replicating Bruce Grobbelaars legendary shootout antics of 1984.
Villarreal 1-0 Inter (2005/06 quarter-final second leg)
In just their third season in a major European competition, and their first in the Champions League, Villarreal went all the way to the semi-finals, getting there by knocking out Inter.
The Spaniards lost the first leg at the San Siro 2-1, but that away goal made all the difference in the end, after defender Rodolfo Arruabarrenas second-half header clinched a 1-0 home second-leg victory for Manuel Pellegrinis Yellow Submarine.
Barcelona 1-2 Rubin Kazan (2009/10 group stage)
Had this result come at the end of the group stage with Barcelona already safely through and resting players, it wouldnt have been such a surprise but it happened just three games in, with Pep Guardiolas defending champions at their star-studded full strength.
Rubin Kazan attempted only three shots to Barcas 22 at the Camp Nou but two of them ended up in the back of the net, Aleksandr Ryazantsev and Gokdeniz Karadeniz registering either side of Zlatan Ibrahimovics equaliser to seal a famous triumph for the Russian outfit.
Inter 2-5 Schalke (2010/11 quarter-final first leg)
Schalke were struggling in the Bundesliga but had managed to reach the last eight of the 2010/11 Champions League. Surely theyd come unstuck against holders and Serie A high-flyers Inter at the San Siro, though?
Anything but Jose Mourinhos Nerazzurri led inside 25 seconds through Dejan Stankovics stunning volley over a stranded Manuel Neuer from near the halfway line but Ralf Rangnicks underdogs battled back in astonishing fashion, an Edu brace among their five goals, before winning the second leg 2-1 to progress 7-3 on aggregate.
Basel 2-1 Manchester United (2011/12 group stage)
Despite an underwhelming group campaign, Manchester United knew that a point from their final match away to Basel would see them through to the last 16 in 2011/12.
But Sir Alex Fergusons team, who had claimed yet another Premier League title the previous season, couldnt manage it, Marco Streller and Alexander Frei getting the job done for the Swiss side and rendering Phil Jones late goal nothing but a consolation.
APOEL 1-0 Lyon APOEL won 4-3 on penalties (2011/12 last 16 second leg)
APOEL made history in 2012 as they became the first Cypriot side to reach the Champions League quarter-finals, beating Lyon on penalties after a 1-1 aggregate draw.
The Nicosia-based outfit took this tie to a shootout through Brazilian Gustavo Manducas goal nine minutes into the second leg and didnt falter under the ultimate pressure, converting all four of their spot-kicks to advance to the last eight.
Celtic 2-1 Barcelona (2012/13 group stage)
Celtics Champions League record has not been great on the whole, but the Old Firm giants enjoyed one of their better campaigns in 2012/13, defeating the mighty Barcelona en route to the last 16.
Lionel Messi scored late on for Barca at Celtic Park, but goals from Vincent Wanyama and Tony Watt had already done the damage for the hosts who triumphed despite having a mere 27% possession, completing 303 passes to their opponents 999.
Roma 3-0 Barcelona (2017/18 quarter-final second leg)
Trailing 4-1 from the first leg, Roma had hope as they prepared to host Barcelona in the 2017/18 quarter-finals but only a glimmer of it.
As it turned out, a glimmer was all the Giallorossi needed on a memorable night at the Stadio Olimpico, as goals from Edin Dzeko, legendary captain Daniele Rossi and in the 82nd minute Kostas Manolas stunned the multiple European champions and sent Eusebio Di Francescos team into the semis on away goals.
Real Madrid 1-4 Ajax (2018/19 last 16 second leg)
The 2018/19 Champions League saw a number of remarkable comebacks, one of them coming as Ajax upset holders Real Madrid to book their place in the quarter-finals.
Having lost the first leg in Amsterdam 2-1, Erik ten Hags underdogs romped to a 4-1 win at the Bernabeu to triumph 5-3 on aggregate Hakim Ziyech, David Neres, Dusan Tadic and Lasse Schone getting on the scoresheet.
Young Boys 2-1 Manchester United (2021/22 group stage)
Manchester United were humbled in Switzerland once again in 2021, blowing a 1-0 lead to lose away to Young Boys in their opening group match.
Jordan Pefok won it for the hosts in the fifth minute of stoppage time, sparking delirium in the Swiss capital of Bern. United ultimately won the group while Young Boys finished bottom, but this was no less momentous a result.
Real Madrid 1-2 FC Sheriff (2021/22 group stage)
Real Madrid ended up winning yet another Champions League in 2021/22, but they didnt get through the campaign without suffering a monumental upset at the hands of Moldovan minnows FC Sheriff, making their debut in the competition.
A Karim Benzema penalty cancelled out Jasurbek Yakhshiboevs opener in the Spanish capital, but Sebastian Thills thumping 90th-minute strike secured the biggest win in Sheriffs history. Cue bedlam in one corner of the Bernabeu.
Maccabi Haifa 2-0 Juventus (2022/23 group stage)
Maccabi Haifa had sprung a Champions League shock before, beating a weakened Manchester United side 3-0 in 2002 but downing a full-strength Juventus side represented a considerably bigger achievement for the Israeli club.
Omer Atzilis brace did the damage against the former European champions who, despite being in something of a rut at the time, still boasted stars such as Leonardo Bonucci, Adrien Rabiot and Angel Di Maria and left them on the brink of elimination from the competition.
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