A penalty early in the second half sent St Mirren on their way to a disappointing opening weekend score on Saturday.
The Buddies were eventually beaten 3-0 by Inverness Caledonian Thistle away from home with Lennon suggesting the questionable decision for handball against David van Zanten in the 48th minute killed his players.
"In the first half, I thought the players showed a great hunger and character," he said.
"I told the players at half-time I wanted more of the same, but how cruel football can be.
"The penalty decision went against us, which the players felt aggrieved about, and it seemed to affect us.
"Just 60 seconds later we are 2-0 down through a comedy of errors and then we lose a third goal.
"We worked really hard in the first half, but we let the goals we lost early in the second half affect us when we should have realised there was still enough time to get something back."