Chasing a target of 184 to win, the World XI only managed 150-8 at Lahore's Gaddafi Stadium to concede the series to the home team by 2-1.
David Miller and Thisara Perera scored 32 each while Hasan Ali took 2-28.
Pakistan opener Ahmed Shehzad had earlier missed his second Twenty20 international century when he fell for 89. His 55-ball knock included eight fours and three sixes.
Babar Azam made a 31-ball 48 with five boundaries and added 102 for the second wicket with Shehzad.
Pakistan won the first match by 20 runs on Tuesday before the World XI fought back with a seven-wicket victory on Wednesday to set up today's decider.