The Hoops boss started with a back three of Efe Ambrose, Thomas Rogne and Kelvin Wilson but changed it to a back four after Leigh Griffiths rounded Parkhead goalkeeper Fraser Forster after eight minutes before scoring the winner from an acute angle with his 14th goal of the season.
The visitors dominated almost totally thereafter, and Lennon said: "Frustration is the key word. First of all I would like to say it was a great atmosphere and a great game, played in a great spirit. But I am not disappointed in our performance at all. I am disappointed with the goal, obviously, and I am disappointed with my own formation, which I changed, so I will take the blame for that."
He added: "We had two formations set up and I chose the wrong one by the look of it.
"The three didn't really work for us today and once we went to a flat back four we were more in control and for 70 odd minutes we dominated the game. I was disappointed with the final ball and composure in front of goal but on another day we would have won the game comfortably."
Pat Fenlon claimed the win was his best result since taking over as manager just over a year ago as he looked forward to the Edinburgh derby against Hearts in the new year
The Irishman said: "That's probably the biggest win since we've been here.
"To beat Celtic is a fantastic achievement, after the run they have been on of six or seven wins and after qualifying for the last 16 of the Champions League, it is a big result.
"The win against Hearts a few weeks ago was a massive result and I think the players will take a lot of confidence from this result.
"It will give the players a lift (ahead of the Hearts game)."
- Sports & Recreation
- Leigh Griffiths
- Efe Ambrose
- Kelvin Wilson
- Thomas Rogne