PSG, who were seeking their sixth consecutive crown, hadn't tasted defeat in the competition since 27 November, 2012.
Back then they went down in the quarter-final to Saint-Etienne at the Stade Geoffroy-Guichard. The match ended 0-0 after extra-time and PSG – then under Carlo Ancelotti's stewardship – lost the penalty shootout 5-3.
Fast forward just over six years and spot kicks were again PSG's undoing in a quarter-final. They conceded three of them in the last 30 minutes of regulation time against Guingamp.
With the score at 0-0 after 60 minutes, PSG full-back Thomas Meunier tripped Ludovic Blas in the penalty area. Marcus Thuram failed to punish the error as he blazed his penalty over the crossbar.
That reprieve appeared to galvanise the hosts. Meunier converted immediately from sinner to saint when he provided the cross which allowed Neymar to head PSG into the lead.
But with nine minutes left, Juan Bernat fouled Marcus Coco in the penalty area. Referee Benoit Bastien checked with the video assistant referee to verify the infringement. Yeni Ngbakoto took responsibility and levelled.
And in stoppage time Bastien pointed to the spot for the third time after Thilo Kehrer tripped Thuram.
The 21-year-old displayed remarkable nerve to step up and slot past Areola. The Parc des Princes faithful was stunned into silence as Thuram disappeared under a pile of his teammates.
No French side had shown such temerity this season.
"We quite like cup competitions," deadpanned Guingamp coach Jocelyn Gourvennec, who led the club to the 2014 Coupe de France. "To come to the Parc des Princes and win, something extraordinary was needed. And that's exactly what has happened.
"I've never been in a match in which a team has given away three penalties in one half. It must be rare but it has allowed us the chance to progress."
Guingamp will be joined in Thursday's draw for the League Cup semi-finals of by Monaco, Strasbourg and Bordeaux.
"We know that in the cup anything can happen," said Thuram. "We knew how to hinder PSG."
Only Liverpool had conquered Tuchel's men this season. That was in September 2018 in the group stages of the Uefa Champions League, the title that Tuchel was hired to bring to PSG for the first time.
"We had so many chances to win the match. We should have scored at least three goals but we didn't do so," Tuchel told Canal+ Sports. "I think we played with too much confidence and we didn't seem eager to finish the match.
"We've lost a match – our first this season in France – and the chance to win a trophy and that's hard to take," he added.
So, after the marvels of 2015, 2016 and 2018, there won't be the domestic treble in 2019 for PSG.
"You always learn something when you lose," added Tuchel. "You grow and get more experience. I hope this defeat was only an accident."
Only a monumental catastrophe will deprive PSG of their sixth French title in seven years.
As they prepare to face Amiens on 12 January for their 18th league game of the 2018/19 season, PSG are 13 points clear of second placed Lille who have played two games more.
PSG are also into the last eight of the Coupe de France and the last 16 of the Champions League.
Tuchel still has the chance to do something remarkably different.