The East End of Glasgow exploded in the 21st minute when midfielder Victor Wanyama headed the Hoops into the lead.
And the ground erupted in the 83rd minute when 18-year-old Tony Watt raced away to score the second, leaving Lionel Messi's late strike a consolation.
Parkhead witnessed one of its greatest nights, and manager Lennon could hardly suppress his joy, saying: "It was one of the greatest nights in the club's recent history.
"It was very poignant at our 125th anniversary, one to play Barcelona in such a prestigious game and two, to win the game under huge difficulties with the squad decimated by injuries and illness.
"The players are heroes, they are heroes to me -- I can't speak highly enough of their performance, and they will go down in the history books of the club as the team who beat probably the best team in the world.
"Everyone goes on about tactics but football is about players and they have covered themselves in glory."