Ireland came within minutes of claiming an historic draw, and could even had beaten the All Blacks, only for Dan Carter to land a match-winning drop-goal at the death.
O'Gara reckons there was plenty to build on from the agonising loss but fears the World Champions will be much improved in Hamilton.
"We've shown we're competitive and I think we'll have to be prepared for a New Zealand backlash," said the veteran fly-half.
"In fairness to New Zealand, they probably felt they beat us in second gear and that they started the game in second gear.
"They shouldn't have won at the weekend, they were down a man, they were under the cosh, but they won the game.
"They'll be smarting now and they'll probably start in fourth gear on Saturday."
The Irish performance in Christchurch was much improved from their showing in the first Test in Auckland where they crashed to a 42-10 defeat.
And O'Gara admits Ireland must find a level of consistency in their performances.
"The pleasing thing about last weekend is we put ourselves in the position to win, but we didn't get over the line," said O'Gara.
"You can't have fluctuations like that. You've got to have your values and your standards and keep hitting them."