Czech Republic international Kovac was booked for a foul in the 18th minute and was lucky to escape a second yellow after a late challenge on Petrov on the hour mark.
Kovac was substituted minutes later by Gianfranco Zola and O'Neill felt that had Petrov remained grounded, rather than jumping to his feet after the challenge, there could have been a very different result.
"My own view on that is that Stiliyan Petrov basically kept him on the pitch by getting up quickly," O'Neill said. "If Stiliyan Petrov had stayed down on the pitch, had stayed down from the tackle there's no doubt that the player would have been sent off. But he got up quickly and I think Stiliyan Petrov saved him. And well done Stiliyan!"
After criticism in some quarters that his players go down too early, with Gabby Agbonlahor booked for diving in the Carling Cup clash with Blackburn last week, O'Neill was keen to defend the integrity of his team.
"This idea that we have a couple of divers in our team, like Gabby and Ashley Young, I hope that eventually gets washed away with the rest of the nonsense that goes with it," O'Neill said.
"It looked a bookable offence and I think Stiliyan did well for him, I must have a word with him later on."
Petrov, who was involved in a couple of skirmishes during the 0-0 draw, admitted that on another day, Kovac could have been given his marching orders.
"It's up to the referees to make the decisions and there's a lot of pressure on them," the Villa skipper said. "Yeah, he could have been off but he stayed on and things like that happen.
"Maybe next time, we'll have a little bit more luck, a player on the opposition team will get off and we'll be given an advantage. That didn't happen yesterday."