DUBAI - Sri Lanka were off to a solid start but faltered against a determined Pakistan bowling attack as they lost wickets in quick succession in the middle of the innings.
Young paceman Hasan Ali finished with a career best 5-34, while spinner Shadab picked up two key wickets.
Skipper Upul Tharanga top-scored with 61 as Sri Lanka lost their last nine wickets for 106 runs.
Thirimanne, Siriwardana and Vandersay were dismissed after contributing a mere 30-runs to the scoreboard.
Dananjaya was quickly dismissed on his second ball after just scoring a run.
Hasan Ali claimed the wicket of Niroshan Dickwella as he clean bowled the Sri Lankan opener for 18 runs.
The second wicket fell when Shadab Khan caught D Chandimal leg before for 19 runs.
Sri Lanka lost its third wicket when skipper Tharanga was dismissed by Shadab for 61 runs.
Uncapped Imam-ul-Haq is in for Ahmed Shehzad, who failed to perform with the bat in the opening two matches of the series.