The home team was looking down the barrel at 215-9 but Holder hammered seamer Wahab Riaz for a six and a four, and then ran the required two runs off the last delivery as West Indies finished at 229-9.
Misbah-ul-Haq earlier scored 75 in Pakistan's total of 229-6. Off-spinner Saeed Ajmal had all but sealed the match for Pakistan with 3-36 by removing top-scorer Lendl Simmons (75) and captain Dwayne Bravo (13) in quick succession before Riaz came in for a hammering.
The series is tied 1-1 with the last two matches at St. Lucia on Sunday and next Wednesday.
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