The 20-year-old Sadaqat, playing in just his second ODI, hit 75 off 46 balls, and grabbed 3-23 with his left-arm spin to be an easy pick for player of the match in Dhaka on Friday.
After Sadaqat, Pakistan lost their last seven wickets for 43 runs and were bowled out for 274 in 47.3 overs.
Lightning and a hailstorm then delayed play for well over two hours and Bangladesh's target was revised to 243 in 32 overs.
But the hosts were never in the hunt, being bowled out for 114.
Bangladesh won the first ODI by eight wickets after a new-look Pakistan with four debutants were also bowled out for 114.
The series decider will be played on Sunday at the same venue.
Bangladesh were 3-27 and Pakistan skipper Shaheen Shah Afridi had two wickets when the long delay started.
On resumption, Sadaqat trapped top-scorer Litton Das (41) lbw in his second over; Afif Hossain was brilliantly snapped up low by Salman Ali Agha at midwicket and Rishad Hossain was clean bowled by a superb arm ball.
Fast bowler Haris Rauf, the only change by Pakistan from the first game, then cleaned up the tail with 3-26 and Bangladesh were dismissed in 23.3 overs.
Left-handed batter Sadaqat also dominated all three Bangladesh pacers and even took on Nahid Rana by smashing the fast bowler over his head for a straight six in his first over.
In total, he launched five sixes and six fours and provided a strong start of 103 runs with Sahibzada Farhan (31) in 13 overs.
The experienced pair of Agha (64) and Mohammad Rizwan (44) also put on a 109 partnership.
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