Seales leaves Pakistan struggling at 86-4 in weather-hit first Test
At tea, Saud Shakeel was unbeaten on 33 and Mohammad Rizwan on 18, repairing the innings with an unbroken 40-run stand for the fifth wicket after Pakistan won the toss and batted.
Early morning fog delayed the toss and the first two-and-a-half hour session was wasted.
Pakistan skipper Shan Masood seized the chance to bat first on a dry and grassless Multan Stadium pitch that was expected to turn from the early stages.
Both teams started with three spinners and a single frontline fast bowler, and the tourists opened the bowling with left-arm spinner Gudakesh Motie alongside Seales.
It was Seales who provided the breakthrough, forcing an edge off debutant Muhammad Hurraira to wicketkeeper Tevin Imlach in the sixth over. Hurraira scored six.
Three overs later, Motie dismissed Masood off a faint edge to the wicketkeeper for 11 before Seales trapped Kamran Ghulam leg-before with a sharp incoming delivery for five.
It became 46-4 when Babar Azam edged Seales behind the wicket for eight, continuing a poor run of scores at home from Pakistan's premier batter.
The two-match series is part of the World Test Championship's third cycle (2023-2025). Pakistan currently rank eighth and the West Indies ninth and last.