The Buddies were 2-0 up and cruising at Tannadice last Saturday when Brian Graham pulled a goal back from a blatantly offside position.
But Lennon revealed he has not bothered to call the Scottish Football Association's head of referee operations Fleming - claiming he was more annoyed by his players' reaction to the set-back.
He said: "No I wouldn't bother contacting the SFA about that. What's the point?
"It won't change the result of the game. Mistakes happen.
"I never get too high with referees, I never get too low with them either.
"We were bitterly disappointed with the decision and it was a difficult pill to swallow. But complaining about it won't get us anywhere. It won't change the outcome.
"What I was disappointed with was the reaction of our players.
"We let the mistake affect us and we need to learn from that. For the 78 minutes before that, we were unbelievable and in total control.
"But when we let it affect us and fail to show our true qualities, we become vulnerable. We become ordinary."
Lennon knows his side will not be allowed to let their concentration slip when they face Celtic at Parkhead on Saturday.
The runaway Scottish Premiership leaders are just three wins from their third successive title but the second-bottom Saints need all the help they can if they are to avoid a relegation play-off at the end of the season.
Lennon said: "Celtic have had a fantastic campaign and at times have been phenomenal - untouchable even.
"We could be at our best on Saturday and still lose. What we have to do is work hard and hope one or two Celtic boys have an off-day. Miracles do happen."
Midfielder Kenny McLean has been linked with a summer move to Rangers but Lennon has not given up hope of persuading the out-of-contract Scotland Under-21 cap to stay in Paisley.
He said: "I take these reports with a pinch of salt unless there is a call or fax through to the club letting us know about an offer.
"We put an offer to him but I totally respect the fact he is keeping his options open.
"Kenny is ticking all the boxes right now and if he moves on to bigger and better things then good luck to him."
- Sports & Recreation
- Scottish Football Association
- Nadir Ciftci
- Brian Graham