Sri Lankan batsman Dimuth Karunaratne. PHOTO: AFP
Skipper Angelo Mathews was unbeaten on 24 and with him was Prasanna Jayawardene who was 28 not out.
Sri Lanka lead the three-match series 1-0 after their nine-wicket win in the second Test in Dubai. The first Test had ended in a draw in Abu Dhabi.
Kumar Sangakkara made 52 and Mahela Jayawardene scored 47.
For Pakistan Saeed Ajmal was the pick of the bolwers with 2-62.
Earlier, Pakistan had removed stubborn opener Kaushal Silva before Sri Lanka reached 64-1 at lunch.
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.
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.
Silva - who made 81, 95 and 58 in the series - hit one boundary.
Left-hander Karunaratne has so far hit two boundaries and a six off 91 balls.
Pakistan had 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.
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