Southee took five wickets, including just the third hat-trick in international Twenty20 matches, while Guptill scored 54 in 29 balls as a new-look New Zealand side produced a morale-boosting win.
Guptill's 54 included four sixes, one of which almost went out of the ground, before he was run out when attempting a quick single but was sent back by stand in captain Ross Taylor, who finished on 39 not out and saw the home side to victory.
ScoreBoard
PAKISTAN
Hafeez c McGlashan b Southee 24
Afridi c Southee b Mills 20
Shehzad c M’lshan b Southee 14
Younis c Brownlie b Southee 2
Akmal lbw Southee 0
Alam c Franklin b Styris 9
Razzaq c McGlashan b Southee 1
Gul lbw Franklin 30
Riaz (not out) 30
Ajmal c McGlashan b Mills 1
Akhtar (not out) 8
Extras (LB-1, W-3) 4
Total (for 9 wickets, 20 overs) 143
Fall of wickets: 1-37, 2-58, 3-62, 4-62, 5-62, 6-68, 7-84, 8-110, 9-112.
Bowling: James Franklin 3-0-14-2, Kyle Mills 3-0-35-1, Adam Milne 4-0-47-0, Tim Southee 4-1-17-5, Scott Stryis 4-0-18-1, Nathan McCullum 2-0-11-0.
NEW ZEALAND
Ryder c Younis b Shoaib 6
Guptill (run out) 54
Brownlie c Akmal b Akhtar 5
Styris b Shoaib 7
Taylor (not out) 39
Franklin lbw Hafeez 19
McGlashan (not out) 5
Extras (B-4, LB-1, W-6) 11
Total (for 5 wkts, 17.1 overs)146
Fall of wickets: 1-27, 2-45, 3-55, 4-91, 5-115.
Bowling: Razzaq 1-0-15-0, Akhtar 4-0-38-3, Gul 2-0-16-0, Ajmal 3.1-0-14-0, Riaz 1-0-10-0, Afridi 3-0-19-0, Hafeez, 3-0-29-1.