Captain Salman Ali Agha made 46 as Pakistan reached 9-135 in a match reduced to 15 overs per innings after a delay for a wet outfield.
Shaheen Shan Afridi then bowled a maiden to start New Zealand's innings. But Seifert and Allen hit seven of the next 12 balls for sixes as the hosts launched an assault which helped them clinch the match and a 2-0 series lead with 11 balls remaining.
New Zealand were 2-87 when Allen followed Seifert to the pavilion in the seventh over.
"There's not too much conversation out there to be fair," Seifert said.
"It's just about backing our skills and putting pressure on the bowlers when we can."
Mitchell Hay made an unbeaten 21 to steer New Zealand home and Bracewell hit a four off Jahandad Khan for the winning runs.
New Zealand won the toss and were eager to bowl first on the University Oval pitch on Tuesday.
Jacob Duffy, who took 4-14 in the series-opener which New Zealand won by nine wickets on Sunday, removed Hasan Nawaz with the fourth ball of the match.
Pakistan reached 1-19 before Ben Sears came on in the fourth over and dismissed Mohammad Haris with his first delivery.
Sears, who missed the Champions Trophy with injury, used bounce effectively and Haris sliced his first delivery to Duffy at third man.
Pakistan were 2-36 after their five-over power play.
Salman took 12 runs including a 75m six from the sixth over bowled by Jimmy Neesham, but spinner Ish Sodhi dismissed Irfan Khan (11) and Khushdil Shar (two) with the fourth and sixth balls of the seventh over as Pakistan slipped to 4-52.
Salman stepped up the pace, taking 10 from the eighth over bowled by Sears and 13 from the ninth bowled by Sodhi which lifted Pakistan to 4-76. But he fell in the next over, caught by Mark Chapman at deep mid-wicket off Sears.
Shadab (26) took up the attack, hitting Sears for six in the 10th over while 14 came from the 11th over bowled by Bracewell.
Shaheen Shah Afridi made 22 from 14 balls as Pakistan added 25 runs from the last three overs.
"It was a better game than last game," Agha said.
"We batted better but we still need to be better finishers."
