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The French side had won the first leg 2-0 at Old Trafford, but then proceeded to lose 1-3 at the Parc des Princes - in part thanks to a backpass that Romelu Lukaku latched onto ahead of Buffon and scored in the opening minutes.
The Italian's nightmare evening wasn't over there, and he spilled a Marcus Rashford shot which Lukaku capitalised on to double his tally after half an hour. This was after Juan Bernat had hit the back of the net to put PSG back on equal footing.
A last minute Rashford penalty completed the comeback, which saw the Red Devils go through to the Champions League quarter-finals.
Last time we played PSG- :beginner: Totally Man Utd:tm: :beginner: (@TotallyMUFC) October 20, 2020
Lukaku saved us with 2 goals.
It's no wonder then that the legendary goalkeeper is still thinking about the night, and he told Marca this week that he can't get past the mistakes.
It will have been particularly gutting for the 42-year-old, having not won the Champions League despite his incredibly successful career.
"In Manchester we won a huge game -2-0 with goals from Kimpembe and Mbappe] with a great show of force. Unfortunately I blame myself for an incredible mistake," Buffon said.
"A mistake that, with the experience I had, I should not have made.
THE UNTHINKABLE HAS HAPPENED!- Football on BT Sport (@btsportfootball) March 6, 2019
Marcus Rashford converts from the spot after VAR awards the visitors a late, late penalty!
Man Utd are through, PSG are out. Unbelievable! :scream: pic.twitter.com/03NMqxQUj6
"We thought it was a formality and I got carried away. It was as if that match was of little value because we had already won 2-0 in the first leg and they, the poor, had two players available and nine young people."
Buffon has now returned to Juventus, and will be hoping for another chance to break his Champions League duck with Cristiano Ronaldo leading the line in Turin.