The Australians have strung their most consistent rugby in years together, opening the four-nations tournament with two wins and a loss.
That includes a rousing 28-24 comeback victory over Argentina six minutes into injury time last week in Townsville.
Last year the Wallabies kicked over a last-gasp penalty to edge Argentina 20-19 in their first Test, but the hosts responded in emphatic fashion.
McDermott was part of the match-day squad in Sante Fe that suffered a record 50-point loss to the Pumas, the home side scoring seven second-half tries.
The No.9 expected Argentina to mount a similar fightback on Saturday at Sydney's Allianz Stadium, with the match a sell-out.
"We know, particularly from that first half, the Argentinian side are going to be unbelievably good this weekend," McDermott said.
"They're going to be disappointed with how that game finished because they probably should have closed it out and they didn't."
While coach Joe Schmidt was pleased with his team's form, the Reds playmaker said there was still plenty to work on with complacency not part of the picture.
"Complacency's never really been an issue for us - we only have to look at last year, for example," McDermott said.
"We had a really good performance and then they put 60 on us the next week so there's absolutely no complacency from our point of view.
"Obviously Joe, post-game, was happy with the result but the actual game itself we've got a hell of a lot to work on and that's what we've been doing.
"We've been real with the feedback we've received and some honest chats around where we need to get better.
"But it's great because we're turning in the right direction and we've got to make sure every single day we continue to do that."
McDermott said producing consistent performances was an indicator of their growth under Schmidt, with the Australians in the hunt in each match this year, win or lose.
"We've been a lot more consistent this year than we were last year under Joe," the 26-year-old said.
"That's definitely something we're working towards - we want to be a consistent team that performs week in, week out regardless of who we go up against.
"We saw that against South Africa twice whilst we didn't get the victory in the second game we were there, thereabouts and we had a chance to win it, we just weren't good enough.
"That's what's burning in the background, those tight results, where we know on our day when we actually put all the pieces together, we win games.
"We've got to make sure we're putting those pieces together."
Schmidt will name his team on Thursday with McDermott vying with Nic White to start at No.9.
McDermott said Tom Lynagh was still troubled by a hamstring niggle but the flyhalf was available for selection.
