The former Ireland flyhalf, who won the first of his six Lions caps in the opening match of the 2013 tour of Australia at Lang Park, dismissed talk of Andy Farrell's team being overwhelming favourites for the match.
"We don't pay too much attention to the bookies odds or what people are saying," he told reporters at Lang Park on Friday.
"We're just concentrating on tomorrow and trying to put a great performance out there.
"Because that's what it's going to need, a great performance, not a good performance, to beat this Australian team.
"They're a proud nation, they're a top class team, well coached. And we need to get our best version of ourselves out there tomorrow."
The Lions won the 2013 series 2-1 but only got off to a winning start in Brisbane after Australia's Kurtley Beale slipped over while attempting a late penalty kick that would have given the Wallabies victory.
"I think the occasion, the atmosphere, the crowds, that's the thing that always lives with you," Sexton said, recalling his Lions debut.
"Obviously when Kurtley slipped and missed the kick, obviously the euphoria that we felt. But again, it just shows the margins of professional sport and top level sport like we're going to witness tomorrow.
"It's going to come down to something small like that, and hopefully we'll be on the right side of it."
Sexton, who played all three tests in 2013 and in the drawn series in New Zealand four years later, said the Lions were expecting Australia to come hard at them on Saturday.
"They'll have been in camp over the last few weeks getting ready for us, and they had a game against Fiji a couple of weeks ago that they'll have learned a lot from," he said.
"There's you can talk about all the different ifs and buts and permutations, but ultimately, once you step onto the pitch tomorrow, no one remembers it, and we just get on with the game."
