No team had ever come back from a four-goal first leg deficit in the history of the Champions League. That is until Barcelona did it on Wednesday, stunning PSG and writing themselves into soccer lore.
What are the most incredible comebacks the Champions League has ever seen?
Manchester United vs. Bayern Munich, 1999 final
Manchester United were down a goal heading into stoppage time of the 1999 Champions League final. Their quest for the first treble in English history was going to fall short.
That is until Teddy Sheringham scored in the 91st minute. But Manchester United didn't even need extra time in this one because Ole Gunnar Solskjaer's stunning goal in the final second propelled the Red Devils to their first European crown in 31 years, not to mention that historic treble.
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Barcelona vs. Chelsea, 2000 quarterfinals
Chelsea weren't a powerhouse in 2000 and their 3-1 win at Stamford Bridge in the first leg shocked most observers, but Barcelona were still favored to come back at the Camp Nou.
A pair of first-half goals brought Barcelona level, 3-3, but then Tore Andre Flo scored and Chelsea were back in front. Dani Garcia came to the Catalans' rescue with an equalizer, but that only forced extra time. Barcelona still had work to do, but they did it. Rivaldo and Patrick Kluivert's goals pushed Barcelona to a 6-4 aggregate victory.
Later, Barcelona's Gabri Garcia called the second leg, "the greatest night of my life."
Monaco vs. Real Madrid, 2004 quarterfinals
Real Madrid were two years removed from being champions of Europe and had been in the semifinals the year before. Plus, they're Real freaking Madrid, so when the Merengues won 4-2 in the first leg, Monaco looked done for.
When Raul scored first in Monaco to make it 5-2 on aggregate, it really looked like the tie was ever, but Ludovic Guily's goal just before halftime gave Monaco hope. Then Fernando Morientes started the second half with a goal. All of a sudden, Real Madrid were on the ropes and in danger of blowing a spot in the final four. Giuly made sure they did just that, finding the net for the second time on the night and sending Monaco past mighty Real Madrid on away goals.
Deportivo La Coruna vs. AC Milan, 2004 quarterfinals
AC Milan were the reigning champions and thrashed Deportivo, 4-1, in the first leg at the San Siro. It was a demolition and Milan could have easily won by more.
It looked like Milan would coast into the semifinals in search of another Champions League title, but Walter Pandiani, Juan Carlos Valeron and Albert Luque all scored before halftime in the second leg and Milan's lead had disappeared. Deportivo were already set to go through on away goals, but Gonzalez Fran came off the bench and scored with 14 minutes left to make it 5-4 and put Deportivo past the defending champs.
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Liverpool vs. AC Milan, 2005 final
Milan had jumped out to a 3-0 halftime lead, presumably ending the final after just 45 minutes. But Liverpool mounted a comeback right out of the break, scoring three times by the 60th minute to bring things level. With neither team able to break the 3-3 deadlock, they went to penalties and it was there Liverpool were clinical making three out of four penalty kicks to win and cap the miracle in Istanbul.
Chelsea vs. Napoli, 2012 round of 16
Chelsea looked like a dreadful team. They weren't going to finish in the Premier League's top four and had already fired Andre Villas-Boas. Losing 3-1 at Napoli in the first leg looked like the start of a Champions League elimination that would have fit in a season to forget, but Didier Drogba and John Terry got the tie level at 3-3 back at Stamford Bridge.
A goal by Gokhan Inler not only gave Napoli the lead again at, 4-3, but it brought them even on away goals. Chelsea were back in a hole, but Frank Lampard's penalty at least earned Chelsea extra time. There, Branislav Ivanovic found the back of the net and the Blues were quarterfinal-bound.
The season proved to be far from one to forget. As bad as they were in England, Roberto di Matteo led Chelsea past Benfica, Chelsea and Bayern Munich (in Munich) to become one of the most improbable Champions League winners ever. And it started with the comeback against Napoli.
Barcelona vs. AC Milan, 2013 round of 16
When Barcelona lost 2-0 at AC Milan, they looked done for. No team had ever recovered from a two-goal deficit in the first leg of a Champions League tie without an away goal before. But Barcelona didn't need the away goal, or even much dramatics because they crushed Milan in the second leg.
Lionel Messi scored the first two goals, then David Villa and Jordi Alba added their own as Barcelona moved on.
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Manchester United vs. Olympiacos, 2014 round of 16
This was less a Manchester United comeback and more a Robin van Persie comeback. Olympiacos won the first leg, 2-0, sending the tie back to Old Trafford.
With a packed house at the Theater of Dreams watching, van Persie first connected from the penalty spot at the 25-minute mark. Then he scored once more just before halftime. Finally, the Dutchman added a third for his first ever Champions league hat trick, completing the one-man show that sent Manchester United marching on.
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Bayern Munich vs. Porto, 2015 quarterfinals
Some comebacks are amazing because of their unlikelihood or the shock factor. This isn't so much that because Bayern Munich were a powerhouse in 2015 and should have beaten Porto, but how they did it was mesmerizing.
After losing 3-1 in Portugal, Bayern Munich throttled Porto back at the Allianz Arena. The Bavarians scored five goals by halftime. When Porto found a second-half tally to make it 6-4 on aggregate, it was really just cute. But Bayern couldn't handle the cuteness so Xabi Alonso scored one more in the most clinical and thumping of comebacks ever.
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Barcelona vs. Paris Saint-Germain, 2017 round of 16
No team had ever come back from four goals in the history of the Champions League and Barcelona had to do that without an away goal. But amazingly, turning around their 4-0 first-leg deficit wasn't their most shocking accomplishment in this tie.
Three goals brought Barca within one after just 50 minutes, but Edinson Cavani's 62nd-minute goal didn't just stretch the PSG lead to two -- it gave them an away goal. Barcelona needed three goals to advance, and that was still the case in the 88th minute. They had no chance.
Then Neymar scored on a beautiful free kick. And he made a penalty. The tie was even, 5-5 on aggregate. But that wasn't enough because PSG were going through on away goals. That's when Sergi Roberto came flying in with the most improbable of goals to complete the most impossible of comebacks.
From 4-0 down. With three goals in seven minutes. Barcelona had pulled off the most amazing comeback in Champions League history.