Paceman Mohammad Talha had Silva caught behind off a sharp outgoing delivery before Dimuth Karunaratne (34) and Kumar Sangakkara (12) batted comfortably on a flat pitch after Sri Lanka won the toss and batted.
Pakistan, desperate to level the three-match series after losing the second Test in Dubai by nine wickets, will look for more wickets in the second session with spinners Saeed Ajmal and Abdul Rehman.
Talha, one of three changes in Pakistan's line-up, forced an edge off Silva in his second spell to leave Sri Lanka 31-1.
Left-hander Karunaratne has so far hit two boundaries and a six off 91 balls.
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Pakistan brought in Rehman, Talha and Azhar Ali in place of Rahat Ali, Bilawal Bhatti -- who was ruled out due to a hamstring injury -- and Mohammad Hafeez.
Sri Lanka, anticipating the pitch to turn on the last two days, handed a Test cap to 31-year-old spinner Dilruwan Perera, leaving out paceman Nuwan Pradeep.
The first Test ended in a draw in Abu Dhabi.