The Hoops icon watched in admiration as the Catalan giants – who he helped lift the Champions League trophy after he ended his seven years at Parkhead – lost 2-1, despite having 89% of possession.
Larsson was full of praise for the guts and determination of the players, and even more fulsome in his acclaim for former team-mate Lennon.
The Swede said: "They had a game plan already set. Over the two games, they did a fantastic job.
"They knew they would not have the ball very much, but that they would always have a chance from set pieces and in counter attacks.
"Neil set up his team perfectly and executed the plan 100%."
Asked if this would provide the platform for Celtic to make it into the last 16, Larsson was unequivocal.
"It has to be," said the Hoops icon. "You can take a lot of positives from the two games against Barcelona. This team is very strong. They play for the club and play for the manager.
"When you have a team like that, the sky is the limit."
Larsson is also aware of the importance of the Celtic support, and revelled in the sight and sound of the backing they gave the team.
He said: "Everybody back home is raving about the Celtic fans.
"It really came through the television. It was nice to hear and really brought back a lot of memories.
"It's unbelievable, if you have not been there, go there, please.
"It is an experience you will not get at another place, especially on European nights.
"Everyone comes out and really helps the team maybe when things are not going that well.
"I don't think the team would have had the energy to go on for 90 minutes plus last night if they did not feel this from the supporters."
Larsson continued: "It's not a myth. Sometimes, when you are running and you might not have the energy, but you feel the roar from the crowd, it makes you go that extra yard.
"That's vital, especially in those games, and especially with the possession Barcelona had last night.
"I don't know how many times they blocked the last pass before Barcelona were on the way through to goal.
"The goalkeeper had a fantastic game as well. Everybody played a little bit better than the normal level, and that's what you need."