"For myself it's just about keeping things simple and sticking to my game plan, which is looking [to play] straight early and expanding from there, not getting too far ahead of myself and waiting for the bad ball," Guptill said.
His run production in the domestic T20 boosted his confidence and he's now feeling good about his prospects of making runs every time he walks out to the crease.
"At the moment I just feel in control of my emotions and my physical state.
"I've just had good confidence over the last few months, that's the big key to it.
"I'm backing my ability a lot more at the moment. I've just got to keep riding that wave."
Guptill, among the cleanest strikers of the ball in the country, is averaging a healthy 38.74 over 55 ODIs.
South Africa are around the corner. Bigger challenges lie ahead. But if Guptill can keep guzzling whatever potion is working right now, he'll be ready for them when they arrive in a couple of weeks.
"The way Martin's playing at the moment is exceptional," his captain, Brendon McCullum, said.
"He's maturing as a cricketer and starting to put into practice the experience he's had at international level."
New Zealand have omitted offspinner Nathan McCullum and left-arm seamer Michael Bates for today's first ODI at Whangarei's Cobham Oval. Bates also missed the opening game in Dunedin but is expected to play at Napier in the third and final ODI on Thursday.
Legspinner Tarun Nethula will make his New Zealand debut, with the 12th man likely to be either Doug Bracewell or Kyle Mills.
Canterbury allrounder Andrew Ellis is expected to get a promotion up to No 7 in the batting order after his encouraging, and brisk, 33 at Dunedin, which put some grunt into an innings which was threatening to sag badly in the second half.
Cobham Oval will become New Zealand's 12th international venue, having received it's international thumbs-up midway through last year, to much local delight.
It is a pleasant setting, sitting next door to Northland rugby's HQ, Toll Stadium, and Northland Cricket has put a pile of work into transforming the ground.
Zimbabwe played a New Zealand Academy XI on the old ground, a couple of hundred metres away, in 1996, the year after the West Indies were due to play a one-dayer against Northern Districts, before it was washed out.
Pakistan had a three-dayer there last summer.
Today will be a good examination for the ground. Hosting a World Cup game or two in 2015 is an ambition. So too a test.
There is also a local hero in the New Zealand side in Tim Southee, club member at Maungakaramea, 18km south of Whangarei.
As for Zimbabwe, they are more comfortable in the shorter forms of the game and should be capable of improvements as this part of their tour progresses.
Their bowling at Dunedin was generally tidy, but the batting leans heavily on captain Brendan Taylor.
He not only needs to make runs, but find support. Tatenda Taibu, Malcolm Waller and the experienced Hamilton Masakadza appeal as potentially the best sources for that.
NZ V ZIMBABWE
Cobham Oval, Whangarei, 11am today
New Zealand: (from) Brendon McCullum (c), Martin Guptill, Rob Nicol, Kane Williamson, Tom Latham, Dean Brownlie, Andrew Ellis, Jacob Oram, Doug Bracewell, Tarun Nethula, Kyle Mills, Tim Southee.
Zimbabwe: (from) Brendan Taylor (c), Stuart Matsikenyeri, Hamilton Masakadza, Regis Chakabva, Tatenda Taibu, Malcolm Waller, Elton Chigumbura, Shingi Masakadza, Keegan Meth, Ray Price, Kyle Jarvis, Tino Mawoyo, Forster Mutizwa, Prosper Utseya, Brian Vitori.
