"There's only probably five players in the world who can produce an innings like that - there's an Australian, a South African and a West Indian, and we're lucky we've got two New Zealanders at the top of the order who can produce an innings like that. Exceptional."
It's not hard to figure out who McMillan had in mind, even though he didn't identify them by name.
AB de Villiers, who has a touch of genius about his batting; the cool cat from Kingston, Jamaica, Chris Gayle; and bristling little Australian opener David Warner were in McMillan's mind. He was clearly chuffed to be able to put the two New Zealand ODI openers in that select group.
There are other international batsmen - Australian skipper Steve Smith, South African Hashim Amla, Joe Root and Alastair Cook of England, Virat Kohli from India and the ageing but still inspiring Pakistani Younis Khan for starters - who sit near the top of any international batting order of merit.
But McMillan is talking specifically about those who go in at, or near, the top and can change an ODI in a matter of balls, rip a game away from opponents.
It is no coincidence that his Gang of Five also boast stellar T20 records too, even if de Villiers and Warner are yet to crack the T20 ton.
Guptill's performance rounded off what McMillan rates "probably the most complete ODI performance we've put together for some time".
"The way the guys went about their work with the ball and in the field set things up and it was after that we needed to finish in style - and that was some style."
New Zealand will want to keep the foot down on Sri Lanka and despite events in the past two games, insist they are strong opponents, who have begun the series poorly. New Zealand want to keep things that way.