"Some are a bit short of runs but we're only two games into this series," he said. "There's plenty of game time ahead. I don't think we're at the stage of panic stations yet, but we're sure they'll come good."
Dan Vettori may be persevered with at No 5 again today. There is a reluctance to shift Corey Anderson and wicketkeeper Luke Ronchi up one spot from their usual positions of No 6 and 7.
If Grant Elliott is again unavailable for family reasons - and there was no definite word on that late last night - and no one else is drafted in, say Dean Brownlie or Anton Devcich, Vettori is the only option.
McMillan bristled at the idea that his old teammate batting that high was an experiment, pointing out he had opened in an ODI before, albeit three times, the last 12 years ago.
"He's got a lot of international runs, has a lot of experience, is there to do a job we needed and he could well do that again tomorrow."
And to those already thinking World Cup, there was a message: that's not central to this team's thinking.
"It's easy to look too far down the track. The World Cup is not our focus at the moment. Winning this series is ... alarm bells aren't ringing within the squad," McMillan said.
Nor should they, but New Zealand will want to get back in the saddle swiftly after being roughly unseated at Seddon Park.
Expect Tim Southee and Mitchell McClenaghan to return today, in Southee's case for his first game in the series. Adam Milne, beaten about in Hamilton particularly by centurymaker Tillekaratne Dilshan, is likely to sit this one out.
Sri Lanka appeal as a team who, once the bit is between their teeth, will be seriously awkward opponents.
Dilshan's classy century in Hamilton may come to be seen as a turning point for the tourists, the innings which ensured their first win on tour and raised the spirits. He had an early letoff but once he hit top gear, he was simply too good.
There's no doubt this trip is helping their cup preparations.
Sri Lanka are playing in conditions vastly different from back home, working out the best strategies come cup time. They are likely to be zeroing in at least partly on their seam bowling options.
The possibility of their mop-haired death overs artist Lasith Malinga not being fit until the start of the World Cup could be a significant worry. No Malinga at his peak will seriously hurt their ability to restrict the heavier-scoring sides.
"It's good experience," captain Angelo Mathews said.
"Malinga is the most experienced guy in our fast bowling lineup.
"We need to get used to the conditions, the bounce, pace and variations and we need to try and manage the workloads of our bowlers.
"They've got to stay nice and fresh for the World Cup."
Swing bowler Nuwan Kulasekara, with 173 wickets in 161 matches, is a tidy operator and slugging allrounder Thisara Perera's record is handy.
However, Sri Lanka are showing they will get good value from their spinners, too.
The blend of Sachithra Senanayake, Rangana Herath and Dilshan look distinctly handy.
It's game on, for sure.
Game plan
Three things New Zealand will want to see at Eden Park today:
• Productivity from batsmen Martin Guptill, Tom Latham and Ross Taylor. Taylor did get 34 in Hamilton but was not his assertive self, while Guptill's ability is not the issue. But he's better than 0 and 10. Latham, 15 and 5, is yet to settle in. The captain can't do it all himself.
• An end to dopey running. One run- out can happen; two at a pinch when things get hectic. Four won't be repeated but best leave the jitters in the changing room.
• Not allowing Sri Lanka's batting champions to get settled. It's cost them twice. Stick tight to the bowling plans.
NZ v Sri Lanka
Third ODI
Eden Park, 2pm today.
New Zealand: (from) Brendon McCullum (c), Martin Guptill, Tom Latham, Ross Taylor, Grant Elliott, Dan Vettori, Corey Anderson, Luke Ronchi, Nathan McCullum, Tim Southee, Matt Henry, Mitch McClenaghan, Adam Milne.
Sri Lanka: (from) Angelo Mathews (c), Tillekaratne Dilshan, Dimuth Karunaratne, Kumar Sangakkara, Mahela Jayawardene, Lahiru Thirimanne, Jeevan Mendis, Thisara Perera, Nuwan Kulasekara, Sachithra Senanayake, Rangana Herath, Shaminda Eranga, Dinesh Chandimal, Suranga Lakmal.
