Southee, 35, took 4-25 as Pakistan were dismissed for 180 after 18 overs in pursuit of 227.
Daryl Mitchell was the top scorer with 61 from just 27 balls and captain Kane Williamson had added 57 from 42 as the Black Caps posted a score of 226-8 from 20 overs.
The Southee's numbers mean he now has 151 wickets in 118 T20 internationals, 11 more than the next player on the list - Bangladesh spinner Shakib Al Hasan.
"Tim has been around for a long time and that's because of his consistent performance over a long period of time," Williamson said.
"But he also adds a lot as a leader in our environment - a calm head and it's pretty good to have him with some fast and nasty young [bowlers]."
Pakistan players struggled to contain the New Zealand batters, conceding 21 fours and 11 sixes.
Debutant Abbas Afridi was the pick of the bowlers, taking 3-34, while skipper Shaheen Shah Afridi finished with figures from 3-46.
Shaheen led the team for the first time since Babar Azam resigned as post in November after Pakistan failed to qualify for the knockout stages of the World Cup.
Babar got the best score for the tourists with 57...
Southee, 35, took 4-25 as Pakistan were dismissed for 180 after 18 overs in pursuit of 227.
Daryl Mitchell was the top scorer with 61 from just 27 balls and captain Kane Williamson had added 57 from 42 as the Black Caps posted a score of 226-8 from 20 overs.
The Southee's numbers mean he now has 151 wickets in 118 T20 internationals, 11 more than the next player on the list - Bangladesh spinner Shakib Al Hasan.
"Tim has been around for a long time and that's because of his consistent performance over a long period of time," Williamson said.
"But he also adds a lot as a leader in our environment - a calm head and it's pretty good to have him with some fast and nasty young [bowlers]."
Pakistan players struggled to contain the New Zealand batters, conceding 21 fours and 11 sixes.
Debutant Abbas Afridi was the pick of the bowlers, taking 3-34, while skipper Shaheen Shah Afridi finished with figures from 3-46.
Shaheen led the team for the first time since Babar Azam resigned as post in November after Pakistan failed to qualify for the knockout stages of the World Cup.
Babar got the best score for the tourists with 57...