Seconds after Stephen Elliott's second-minute header appeared to cross the line before being blocked by Celtic midfielder Joe Ledley, Hoops skipper Scott Brown drove low past Jambos keeper Jamie MacDonald for the opener. Midfielder Victor Wanyama and Ledley made it 3-0 at the interval before striker Gary Hooper concluded the romp on the hour mark.
Lennon said: "Probably (the best) in my time as a manager. I thought we were devastating, powerful, quick on the counter-attack and the intensity and quality of their play was exceptional."
He added: "There is a long way to go but they are growing and that was a big test for us. I feel for Hearts a bit because they lost some big players before the game but they caught us on a good night.
The former Celtic skipper admits his side were let off the hook when referee Willie Collum and his assistant Andy Tait failed to see Elliott's header had crossed the line, and said: "I think we copped a break. Judging by the cameras it looks like it is over the line and the only disappointing thing was we didn't deal with the initial header from the corner.
"Psychologically it might have given Hearts a lift. The ironic thing is we go down the other end and score the goal. But the reaction I got for the rest of the game was magnificent."
Hearts boss Paulo Sergio made more of the incident, saying; "I am very disappointed with the result. What do you want me to say?
"We have been very unlucky with some decisions in the last three games and the referee didn't see it tonight.
"At Inverness we should have had a penalty. Everyone saw it on television but no one on the pitch. We should have had a clear penalty in the cup game against St Johnstone. Nobody saw it again and tonight a goal.
"If you don't see the ball over the line then you should see the handball which is a penalty and a red card. So we were very unlucky."
Source: PA
Source: PA