England ran in four tries as they stormed to a 28-6 victory over the world champions at Hull's KC Stadium.
"We need to go and win the competition but right now we deserve to sit back and not worry too much about next week," said McNamara.
Kiwis coach Stephen Kearney called it a "complete" performance by England.
England led 8-0 at half-time after a try from Tom Briscoe. Ryan Hall, James Graham and Sam Tomkins touched down after the break, while man-of-the-match Kevin Sinfield kicked six goals from six attempts.England have made 'big strides' - Steve McNamara
McNamara added: "I think it was really controlled, measured, efficient, effective - and we knew it had to be that way if we were going to get across New Zealand.
"We had to show patience - I think they held us up over the try-line four times and that was a tremendous effort from them.
"It was a real step in the right direction from us in terms of being able to deal with that.
"We managed to keep the pressure on the opposition, so it was pretty good."
His counterpart Kearney said he thought England have what it takes to beat Australia in the final.
"I thought England played outstandingly well tonight," he said.Steve Kearney makes no excuses for England defeat
"It was a real complete performance from them and they fully deserved the victory. They were very, very good.
"We went a bit away from the structure and game plan, and discipline was a bit of an issue against a very disciplined English side.
"I think England can go into the [Australia] game with some real confidence.
"It's going to be a big ask but if they stick to what they did tonight, I'm sure they'll give Australia a real run for their money."