Bairstow's unbeaten 108 off 48 balls, with eight fours and nine sixes, see Punjab secure the win with eight balls to spare
Afghanistan won the opening the match of the series by 63 runs on the back of a stunning haul of seven for 18 from 18-year-old leg-spinner Rashid Khan, the fourth best bowling figures of all time in the 50-over format.
West Indies, desperate for wins to move up from ninth to eighth spot in the world rankings to avoid having to qualify for the 2019 World Cup, hit back to take a four-wicket victory in the second match.
After a two-hour delay on Wednesday, Afghanistan won the toss for the decisive third match and elected to bat but the rain returned before a single delivery could be bowled. The series was drawn 1-1.