Pakistan carried the momentum into their own innings and even had luck on their side when Kamran Akmal took five runs off the final ball of Mills' opening over.
The very next ball Akmal pulled Mills straight to Guptill at deep square leg but Shahzaib continued the belt New Zealand to all parts of the ground, hitting Ian Butler for two fours and a six in the sixth over.
Adam Gilchrist was trapped lbw by Kyle Mills on the third ball of the match and Chris Martin celebrated his first one-day match in five years by snapping up Simon Katich in his second over.
New Zealand went into the game with pacemen Ian Butler and Kyle Mills replacing all-rounder Jacob Oram and the youthful Tim Southee and it proved a shrewd move as Butler took the Man of the Match award for his 3-19 after Mills struck twice with the new ball.
Gambhir was fortunate to survive a certain lbw appeal when Mills was called for a no-ball with his first delivery of the day, but took advantage of his leg-off to bring up his 10th Test half century.
Hard working Lee Mills drove down the left and pulled the ball back from the touchline for Saunders.
Sidebottom kept the ball moving in the corridor of uncertainty to oust Kyle Mills and Iain O'Brien, who tentatively prodded to first and second slip respectively.
The hosts were frustrated by Vettori and Mills, yet they produced a disciplined effort with the ball and limited the Black Caps to just 52 pre-lunch runs.
Mills' innings, though, came to a close as he too nicked the ball to the slips, Matthew Hayden this time taking the catch off Warne's bowling.
BBC: SPORT | Cricket | Other International | Aussies rally after slump
Vettori and Mills enjoyed some success off Stuart Broad and Monty Panesar, guiding New Zealand past 250, but the second new ball was taken two overs before the break and Sidebottom duly struck with a delivery that swung into Mills and clattered his stumps.
In the next over Mills found some extra lift and movement to unsettle Umar Akmal and have him caught behind first ball as he tried to take evasive action.
Nathan McCullum thumped the last ball of the innings for six to boost the total but New Zealand's prospects looked bleak when Mills over-stepped in his first over, allowing Butt a free hit which he crashed through the covers for four.
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