The greatest upsets in Champions League history

Barcelona's Lionel Messi. (Photo by Paco Largo/Panoramic/Icon Sportswire)

Whether an unlikely result in the group stage, or a shocking takedown in the knockout rounds, there are plenty of chances for upsets in the UEFA Champions League.

A few upsets have sent ripples through the soccer world. Let's count down the five most impactful and stunning upsets that have happened in Europe’s greatest sporting competition.

5. Celtic 2-1 over Barcelona (2012 group stage)

Imagine your club has possession 84% of a match—so much that it was able to attempt nearly 1,000 passes and complete 869. Imagine out-shooting your opponent 25-3, with a talented squad that includes Lionel Messi, Zlatan Ibrahimović, Andrés Iniesta, and Xavi in their prime.

Now, imagine losing that match.

Celtic came away with the victory over the eventual semifinalists. Ben Foster was under siege in goal all night, but made multiple spectacular saves, and it was his long ball that allowed Tony Watt to score the clincher in the 83rd minute.

Victor Wanyama put the hosts in front when he headed one home in the 20th minute from a corner, and Messi’s goal late in stoppage time was not enough to prevent blushes for the Spanish giants.

4. Deportivo de La Coruña 4-0 over A.C. Milan (2004 quarterfinals)

A.C. Milan won Champions League titles in 2003 and 2007 and traveled to Spain with a 4-1 aggregate lead after the first leg. Everyone expected the Rossoneri to walk into the semifinals without much incident, especially since no team had ever come back from a three-goal deficit in the second leg in Champions League history.

Instead they crashed out of the tournament in stunning fashion, as Deportivo set the tone with a goal five minutes into the match and led 3-0 at the break.

Team captain Fran, who had started the match on the bench, came on in the second half to score the deciding goal in the 86th minute. His volleyed shot, which deflected off Cafu and past Dida, put Deportivo in its first semifinal and sent the soccer world into shock.

3. APOEL Nicosia over Lyon on penalties (2012 quarterfinals)

The fact that APOEL was in the Champions League knockout stages was an upset in and of itself. Entering the qualification rounds in August, the club from the tiny island of Cyprus was tabbed at 1000-1 odds to make to the quarterfinal round.

APOEL was also expected to be disposed of quickly by a Lyon side that was in the semifinals a year before, and had won the Ligue 1 title in seven of the previous 10 seasons. Lyon won the first leg at home 1-0, and traveled to Cyprus to see things out easily.

Instead, Gustavo Manduca turned the match on its head with his goal in the ninth minute. He was able to get on the end of a low cross through the box and buried it at the far post. From there APOEL withstood an onslaught from Lyon, and took the match through extra time and into penalties.

The shootout stood at 3-3 before Dionisis Chiotis stopped Alexandre Lacazette’s shot in the fourth round. With APOEL ahead 4-3, Chiotis stopped Michel Bastos’ attempt to finish off one of the most stunning upsets in club-soccer history.

The fairy tale ended in the quarterfinal round, as the upstarts were put to the sword 8-2 on aggregate by Real Madrid.

2. AS Monaco 3-1 over Real Madrid (2004 quarterfinals)

The Galácticos were a stunning collection of some of the greatest talent in the world. In the summer of 2003, Real Madrid brought in David Beckham from Manchester United, adding him to a roster that already featured Raúl, Brazilian striker Ronaldo, Luís Figo, Zinedine Zidane, and Roberto Carlos. Madrid was expected to be the dominant force in the Champions League for years to come.

Instead the club ended the 2003-2004 season without a trophy. Madrid took a 4-2 aggregate lead to Monaco for the second leg of the quarterfinals but was without Beckham, who was suspended.

With 10 minutes to go in the first half, Madrid took the lead on a goal from Raúl. Monaco to leveled in the final seconds of the half through a goal from Ludovic Giuly.

Madrid allowed the hosts to grab a second goal just three minutes after the halftime break, when Fernando Morientes, on loan at Monaco from Madrid, scored against his parent club. Less than 20 minutes later, Morientes found Giuly to put Monaco ahead 3-1 on the night and level at 5-5 on aggregate. Madrid was visibly rattled, couldn't find the goal it desperately needed, and Monaco pulled off the stunning upset.

1. Barcelona 6-1 over Paris Saint-Germain (2017 quarterfinals)

This wasn't an upset based on talent, but rather the overwhelming odds that had to be overcome to secure the result.

While many of the decisions by the referee in the match are still controversial to this day, there is no debating this remains the biggest shocker in Champions League history, even more so because of how the requirements changed once the match began.

Down 4-0 after it was dissected during the first leg in Paris, the Spanish side knew it needed four goals just to force extra time.

Barcelona was given hope when Luis Suárez’s header in the third minute narrowly crossed the line. The club got an own-goal five minutes before the break, and pulled back a third shortly after halftime on a Messi penalty.

Edinson Cavani put PSG on the board with less than a half-hour remaining, but Neymar scored on a free kick in the 88th minute, before a controversial penalty three minutes later saw Neymar make it 5-1. As the referee prepared to blow the final whistle, Barcelona had one final chance, and Sergi Roberto completed the stunning comeback with a 95th-minute volley.