Georgios Samaras scored the only goal of the game to complete a memorable week for the Hoops following their Champions League victory away to Spartak Moscow in midweek.
Lennon told Sky Sports News that his players' desire got them over the line against a spirited Hearts side.
He said: "I'm delighted. It's a magnificent win and tops off a fantastic week for us all.
"The players have been tremendous. You could see there was a bit of fatigue kicking in second half and I totally understand that. We are delighted with the win and the clean sheet.
"We had chances to put the game away and at 1-0 you are always a bit concerned, but Georgios is a big player for us. Gary (Hooper) looked a little bit tired but the strength of the squad is good."
A vital three points for Celtic leaves them two points clear of nearest rivals Hibernian at the summit in Scotland.