When the full-time whistle confirmed their 3-2 aggregate victory, many of Madrid's players dropped to their knees and looked up to the sky, as much perhaps in disbelief as joy.
"Every game is a final now for us in the Champions League and La Liga but today we showed that Real Madrid is alive," said Benzema.
For PSG, it was another epic collapse to add to their growing list of Champions League disappointments, with Mauricio Pochettino's future as coach immediately cast into doubt.
Even with Mbappe, Lionel Messi and Neymar, the Qatari-owned club's wait for a Champions League crown goes on.
"We didn't manage our emotions well. We left ourselves exposed," said Pochettino. "We leave with great pain and disappointment because we didn't score the goals to reflect our superiority over the two games."
Pochettino also fumed at referee Danny Makkelie for not whistling for a foul as Benzema challenged Donnarumma before Madrid's first goal.
"Explaining what happened is easy, there was a foul on Donnarumma during the first goal, and that changed everything," he said.
All eyes were on Mbappe, who was the only player to be cheered by Madrid's fans before the game as they were gifted an up-close preview of the player they hope will be theirs this summer.
Mbappe delivered, scoring a superb goal, not to mention a spellbinding second that was disallowed for offside when he bamboozled Thibaut Courtois with a magical dummy.
But what looked set to become an exhibition of the world's deadliest player instead became another remarkable European night for Real Madrid and another nightmare for PSG.
"We suffered a lot but we endured," said Real boss Carlo Ancelotti. "Karim gave us the chance to score the first goal and then the magic came. From then on, there was only one team was on the field."
Madrid clearly wanted to hit PSG hard from the start and for a while, it worked, Vinicius Junior tearing down the left and Fede Valverde bulldozing through Mbappe.
But the surge was brief, PSG killing Madrid's momentum, pushing them back and taking complete control.
Mbappe sped clear for the first time in the eighth minute, Neymar curling a ball into the space on the left. The stadium held its breath, Mbappe made room but this time hit Courtois.
PSG were comfortable, dictating the play and sensing the trepidation. Madrid had openings, Benzema curling just wide, but all over the pitch they looked slower, heavier, more cumbersome.
Lionel Messi skipped through and scooped wide before Mbappe had his first of two goals ruled out, driving into the corner only to see the flag raised.
The opener, though, felt inevitable and in the 39th minute, it came. Dani Carvajal lost the ball upfield and with Madrid committed, Neymar arced another brilliant pass over the top.
By the time he reached it, Mbappe only had David Alaba in front of him and as he shaped to bend into the far corner he instead fired early, whipping a deadly shot past Courtois and inside the near post.
Madrid tried to reset at half-time but Mbappe carried on where he left off with a brilliant, but disallowed, goal.
He fooled Courtois with an astonishing dummy shot, beating the Belgian without even touching the ball and slammed in. The flag went up but the stadium was astounded.
The game was becoming less a contest, more an Mbappe exhibition but then Benzema, out of nowhere, dragged Madrid back into the tie.
He chased Nuno Mendes' backpass to Donnarumma, who skewed under pressure. Vinicius was able to collect and cut back to Benzema, who slotted home.
It was Luka Modric who inspired Madrid's second, a scintillating run through midfield allowing Vinicius to race clear down the left. He scooped back inside to Modric, whose exquisite reverse pass found Benzema, who finished.
Madrid were level on aggregate, the goal confirmed after a check from VAR. Then just seconds later, incredibly, they were ahead. PSG squandered possession from kick-off, Rodrygo released Vinicius and Marquinhos' attempted clearance found Benzema, who steered into the corner.