The 26-year-old removed Marlon Samuels (37) and Dwayne Smith (0) to rattle the middle order before top-scorer Runako Morton (43) lifted the total from a precarious 79-6 on Thursday.
The West Indies were bowled out one ball before their 50 overs were up, in an innings which had three run outs, including that of captain Brian Lara for 14.
The West Indies, sent in to bat on a slow-paced wicket, were reduced to 2-2 after they lost both their openers, Lendl Simmons and Chris Gayle, without scoring.
Pakistan paceman Umar Gul struck with the second ball, removing debutant Simmons, thanks to a smart catch behind the stumps by wicket-keeper Kamran Akmal.
Gayle, who hit 474 runs in the Champions Trophy in India last month, went in the next over when he edged Rana Naved-ul-Hasan to Pakistan captain Inzamam-ul-Haq at slip.
Inzamam was making his return from a four-match ban imposed for bringing the game into disrepute during the Oval Test fiasco in August.
Samuels and Daren Ganga (21) repaired some of the damage during a 46-run third-wicket partnership before first-change bowler Rao Iftikhar had Ganga caught in the covers off a miscued flick.
Master batsman Lara hit Abdul Razzaq for a boundary and was shaping up well before he was run out after being sent back by Samuels while attempting a single in the 30th over.
Samuels departed in the next over when he edged Rehman to slip for Younis Khan to take a regulation catch. Samuels hit two boundaries during his snail-paced 86-ball knock.
Morton, however, added an invaluable 57 runs for the seventh wicket with Denesh Ramdin (23), hitting four boundaries in his 66-ball knock. He was the ninth man out, holing out to Naved-ul-Hasan, who finished with 2-32.
Pakistan were without their key batsman Mohammad Yousuf, who missed the match to be with his wife, who was expecting a child. The West Indies had to leave out their star batsman Shivnarine Chanderpaul due to a slight knee injury.
The first game of the five-match series was abandoned without a ball bowled due to rain at Rawalpindi on Tuesday.
West Indies 151 all out in 49.5 overs (Runako Morton 43, Marlon Samuels 37, Denesh Ramdin 23; Gul 2 for 19, Rehman 2 for 20, Naved 2 for 32)