The French champion had been trailing 1-0 as the clock ticked toward 90 minutes but two late goals from Marquinhos and Eric Maxim Choupo-Moting turned the tie on its head.
It was heartbreak for tournament underdog Atalanta, which was competing in the Champions League for the first time in its history.
It had seemed Mario Pasalic’s first-half goal was going to be enough but, after a whirlwind three minutes, its players were left crestfallen as the referee blew the final whistle.
The club’s Cinderella run had boosted morale in its home city of Bergamo, which became the epicenter of the Covid-19 outbreak in February.
‘We can’t go home like this’
PSG was heavy favorite ahead of the tie with the disparity between the two clubs stark. Atalanta’s record signing, Luis Muriel, cost an estimated $21 million while PSG’s record signing, Neymar, cost some 12.5 times as much.
However, the far superior side on paper was wasteful for most of the night with Neymar missing two gilt-edge chances in the first half when it looked harder to miss.
It had seemed the team, brimming with talent after the introduction of Kylian Mbappe in the second half, had run out of ideas before striking late on.
“It was a crazy game, a tough game, against a tough opponent. It wasn’t easy. Neymar had a great game,” match winner Choupo-Moting told BT Sport after the match.
“I thought when I was coming on ‘we can’t lose, we can’t go home like this’. I was confident in myself and the team.”
French sensation Mbappe had started the game on the bench as he continues his recovery from injury but his impact in the second half was pivotal.
The 21-year-old injected speed into his side’s attack — a frightening prospect for Atalanta’s tiring legs.
Both he and Neymar provided the assists for the last-gasp goals which fired PSG to its first Champions League semifinal in 25 years.
Apart from his two quite incredible misses, Man of the Match Neymar did show flashes of brilliance all night and was a constant source of creativity going forward.
PSG boss Thomas Tuchel, on crutches for the evening, let out an almighty roar of relief as the night descended into chaos.
Despite his team’s domestic dominance, Tuchel will always be judged on his performances in Europe which, in recent years, have flattered to deceive.
He now has the chance to reach the final when his side faces either RB Leipzig or Atletico Madrid in the next round on Tuesday.
It’s just a shame no fans were in the stadium to watch the memorable tie, with all remaining fixtures being played behind closed doors in Lisbon amid the pandemic.