Johnny Sexton is baffled by "strange" criticism of Ireland and assures they have belief that New Zealand can be dethroned at Tokyo Stadium on Saturday.

Joe Schmidt's side put a shock defeat to Japan behind them to finish second behind the hosts in Pool A with three wins out of four.

Ireland will face defending champions the All Blacks in the quarter-finals this weekend and World Rugby Player of the Year Sexton is surprised with the reaction to their performances in the tournament.

"There's been some negativity around us and we'd feel that's been pretty strange," the fly-half said.

"It's just something that we get a sense of. You get texts saying, 'Keep the head up, we're still behind you.' And you get a feeling that there are some things out there that aren't great. 

"We know things weren't great but it's funny some people trying to compare things to 2007 when they just scraped past Namibia - and we have just beaten Russia 35-0. How there can be comparisons there I'm not quite sure - and in totally different conditions."

Sexton says two victories in the past three encounters with the defending champions have given Ireland confidence they can beat Steve Hansen's men when it matters most.

"We know they're the best team in the world. We can take a little bit of confidence from the fact that we have got that monkey off our back and we've done it a couple of times, which gives us that belief," he added.

"It will be very special if we can get a win because often in a November series they're tired, they've got holidays coming up and maybe they've had a little bit of an excuse.

"But this week they'll be throwing their best at it out there. We've got to concentrate on getting the best version of the Irish team out there and we'll see if that's good enough."