The Lions looked to be on the verge of their first series victory since 1997 before a late try saw the Wallabies snatch the win.
The two teams will now meet in Sydney next weekend in the final and deciding Test of the three-match series.
When asked how he felt after the encounter, O'Driscoll told Sky Sports News: "Very disappointed. But it's not over, we've got a massive week to get ourselves ready for Sydney next Saturday. The momentum is with them, but we won't let that faze us. We've beaten them once."
The Lions and Australia go head-to-head in the series decider at the ANZ Stadium on July 6.