The Parisian side were good value for a 2-0 first-leg win at Old Trafford but slumped to a stunning 3-1 defeat at Parc des Princes as they exited the competition to a last-minute Marcus Rashford penalty.
It echoed back to a similar exit at the hands of Barcelona a couple of years previous, when they threw away a 4-0 first-leg victory and went out after a Neymar-inspired 6-1 defeat at Camp Nou.
Tuchel felt the campaign as a whole was a success but was left to regret that loss to Ole Gunnar Solskjaer’s men.
“It was like having a car crash,” he told beIN Sports . “The light went green and we were hit hard! We wondered what we had done wrong, if we had neglected something. Surely we had neglected something!
“In between the matches, people at my daughter’s school and all around the city were saying: ‘OK, now things are different, we feel it'.
“Everyone thought that we were going to qualify and go further, but we didn’t do it. And I had the impression that, afterwards, everyone said: ‘Ah… it’s not changed, it’s like in previous years'.
“And we thought: ‘No, no, no, it’s not the same'. But we were totally helpless. It was like sand flowing through our hands without being able to hold it back.”
Tuchel explained what an impact the defeat had both on him and the squad.
“In the days that followed, we felt how disappointed we were,” he said. “I spent three days in total darkness, like I had never known before.
“I knew how hard we worked, how difficult it had been to get there, especially after what had happened in previous seasons. I knew the work the squad had put in, how hard the staff had done their jobs.
“I know the amount of work that had been done to get there, to beat Liverpool, to win in Red Star, where they were unbeaten for something like three years, then to become the first French team to beat Manchester United at Old Trafford…”