After they were put in to bat, Shan Masood was the tourists' only casualty of the morning, falling to off-spinner Roston Chase after an hour's play.
Opening partner Azhar Ali (36 not out) was set to resume after the interval alongside Babar Azam (24 not out), their partnership having already produced 51 runs for the second wicket.
West Indies' faster bowlers failed to make the inroads that Jason Holder would have hoped for after he won the toss and had no hesitation in putting the opposition in to bat in heavy, overcast conditions.
It came when Masood, playing his first match of the series in place of the unwell Ahmed Shehzad, reached nine off 30 deliveries and prodded indecisively at a delivery from Chase for Holder to take the straightforward catch at second slip.
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Having failed to score in both innings of the second Test, new batsman Azam found the bowling to be much less challenging than at Kensington Oval and settled into the promising partnership with Ali.
With a 106-run win in Barbados levelling the series, the home side named an unchanged eleven in pursuit of a first Test series win for five years against a team ranked higher than themselves.
Apart from the recall of Masood, fast-medium bowler Hasan Ali is making his debut at the expense of leg-spinner Shadab Khan, who struggled in his first appearance in the second Test.
Pakistan have never won a Test series in the Caribbean on seven previous tours and the significance of the fixture has been magnified by the fact that Pakistan captain Misbah ul Haq and senior batsman Younis Khan are playing their final international matches.