Gul dismissed opener Chris Gayle for 40, took the prized wicket of Brian Lara for nought and also got Ramnaresh Sarwan out for no score on the second day at the National Stadium here on Tuesday.
The West Indies, replying to Pakistan's modest first innings total of 304, reached 131-4 at tea, needing another 173 runs to take the lead.
Daren Ganga (42) and Runako Morton (seven) were at the crease with the West Indies needing a big partnership to press for a series-levelling win.
Gul, who took nine wickets in Pakistan's first Test win at Lahore, returned for his second spell after lunch to get Gayle driving uppishly to mid-on where Abdul Razzaq juggled with the ball before taking it on the second go.
Gayle, who was dropped off Gul by Imran Farhat before lunch on 12, hit six boundaries.
Two balls later Gul produced a beautiful in-swinger which beat the forward push of Lara's bat and sent off-stump cartwheeling. Next over, Gul yorked Sarwan, hitting the middle stump to leave the West Indies struggling at 51-3.
Shivnarine Chanderpaul hit his first ball for four then Ganga hit three boundaries in the next Gul over as the tourists tried to fight back.
Their stand yielded 63 runs for the fourth wicket and it required a brilliant sharp catch by Farhat at silly mid-on off leg-spinner Danish Kaneria to end Chanderpaul's innings at 36.
Pakistan lead the three-match series 1-0 following their nine-wicket win in the first Test at Lahore. The second Test ended in a draw at Multan.
Earlier, Pakistan added 47 runs to their overnight score of 257-7 to be out for 304 in their first-innings.
Corey Collymore, who returned the Windies' best figures of 3-57, removed Kamran Akmal (31) with the first delivery of the second new ball after Akmal hit two boundaries off Daren Powell in the first over of the morning.
Powell provided the visitors with the first breakthrough when he bowled Shahid Nazir without scoring in the second over of the day.
Gul added 32 for the last wicket with Danish Kaneria, who remained unbeaten on seven, before Powell returned for his second spell to finish with 2-83.
Pakistan 304 all out Vs West Indies 131 for 4 (D Ganga 42 n o, Chris Gayle 40, S Chanderpaul 36; Umar Gul 3 for 34, Danish Kaneria 1 for 22)