But the league holders bounced back impressively, beating Monaco 4-1 in the League Cup final and France's two outstanding teams do battle again in the French Cup semi-finals next week as PSG chase a third consecutive clean sweep of domestic honours.
"We are a very close group, we all want the same thing, we flourish together, and that's reflected on the pitch", the French worldwide said.
"We know our qualities and we know what we have to do".
Before his goal tonight he'd joined the likes of Liverpool cult hero Luis Garcia by scoring in his first three, but now he's moved ahead of the rest of the pack.
Monaco are in a comfortable position in the tie, having won the away leg 3-2 and come into the home leg with three crucial away goals. We have a good mix between experienced and young players.
Borussia Dortmund coach Thomas Tuchel during match against AS Monaco.
But any thoughts of a revival were ended by Germain, another replacement, as he converted following a swift Monaco break only 22 seconds after taking the field in place of Mbappe. But it'll be another game and we go to do our greatest to qualify.
Expect Monaco manager Leonardo Jardim to play a more defensive style in the second leg.
Dortmund will be without central defender Marc Bartra, who sustained a wrist injury in the bus attack and has since undergone surgery.
Last week's first leg was postponed by 24 hours after the Dortmund team bus was attacked with explosives on its way to the stadium.
However, their second-leg preparation was also disrupted with Dortmundsaying their bus was held for 20 minutes by local police. Next up is a charge for the Ligue One title plus a Champions League semi-final and I can't wait to see Mbappe plays in those games.
Falcao's diving header, the 27th goal of his comeback season, made it 2-0 in the 17th minute.
The visitors started slowly, and the task of overturning a first-leg deficit became substantially trickier after conceding two early goals and watching Nuri Sahin's curling free-kick strike a post at the other end.
"He won't be able to play all the games at this level".
Back to his best at the right time, he is expected to start alongside Kylian Mbappe, who has 15 goals in his last 15 matches with Monaco.