Pompey were second best for much of the game at the Ricoh Arena and trailed to Gary McSheffrey's well-taken opener after 41 minutes, but they battled to the end and snatched a point when McLeod capitalised on hesitant defending to stab home from close range.
Whittingham was delighted to have halted a run of seven straight defeats and feels it is no more than his players deserve.
"It's massive for us," he said. "The players have put some hard work in on the training pitch and they have got something to show for it now and it might just be that little something that kicks us on. It needs to be.
"It is tough for us because we have a lot to do, we have to make things better than they are and we will work to do that."
He added: "You have to keep going, stay in the game, not get too depressed about what is happening and eventually it paid for us."