The side wants to ensure standards don't slip in the dead rubber, especially with the visit of South Africa looming.
Taking the foot off the pedal saw the Black Caps drop the third one-dayer when they toured Zimbabwe late last year - although the opposition's successful 328-run chase certainly had something to do with it.
"The South African series is obviously fast approaching, but we've still got to make sure we've got our focus on this series,'' McCullum said. "Zimbabwe have shown to us in the past if we take out eye off the ball or if we don't give them the respect they deserve they can come back and take the game to you.''
It would be hard to better Monday's 141-win in Whangarei, certainly with the bat, but that's exactly what McCullum wants.
"I think we've progressively gotten better in the two one-day games so far. Obviously we were a little bit rusty in Dunedin then had a complete performance last game, and this is going to be a good challenge here.''
It remains to be seen whether improving in each game against inferior opposition is the right tune-up to face one of the best teams in world cricket. But you can only beat what's in front of you, and it can only be beneficial for players to take form and confidence into the clash with the Proteas.
"It's hard to know how we're going to be placed when we arrive against South Africa,'' McCullum admitted. "We just have to make sure we're smart and we execute and stand up to the challenge that South Africa will bring when they arrive. But, right now, our focus is on Zimbabwe and that's how it should be.''
McCullum refused to blame Zimbabwe for their performances, which have seen apathy replace acclaim as the main response from the majority of New Zealand's sporting public to yet another big win for the home team.
"I think it's tough for them. They're obviously playing in some foreign conditions. I think we've played very well and obviously put them under some pressure as well.
"[In Whangarei] they had a focus of trying to get some time in the middle and trying to get used to the conditions. I'm sure that would've served their middle order some real value. So we've got to be well aware that they will come back stronger at us in this game.''
Dean Brownlie, who suffered a broken finger in the second game is replaced by Nathan McCullum. The only other change sees Michael Bates making his international debut in place of Tim Southee.
