Ian Bell (64), Jonathan Trott (68) and Joe Root (56) gave England a platform but Mitchell McClenaghan finished with four for 56 as they ran out of steam on 258 all out. Kane Williamson (74) gave the run chase early substance before Brendon McCullum (69no) upped the ante down at number six.
But it was Guptill, after initially retiring hurt on three with a hamstring strain, who returned at number nine to hit 24 runs from just 10 balls to seal victory. There were four fours and a six in his unbeaten 27 and England captain Alastair Cook said: "When you get seven wickets, the normal next man in is a bowler. But it was an opening batter who hits it as well as that, and he played very well."
McCullum did even more damage, hitting six fours and three sixes from 61 balls.
"He's obviously a very dangerous player," added Cook. "Whether he bats at the top of the order or coming in there at six, he's very hard to bowl to. The trick is to try to get him out early."
The whole match was a case of what might have been for England.
"We got ourselves in position to win that," said their captain. "But they got themselves over the line, and we couldn't quite manage to put the pressure on them. We just kept losing wickets at crucial times, and never really got the partnership towards the end of the innings - which could have got us up to 280 or 290.
"We batted well up front, but probably loaded a little bit too much towards the end - put a bit too much pressure on our big hitters. But we got into an okay position to launch; then the guys at the end didn't quite come off.
"I think both sides would have felt disappointed losing that game.
"Both sides kind of got themselves in position to win, and someone had to stand up and grab it by the scruff of the neck - and those two did it for New Zealand."
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