Sri Lankan captain Upul Tharanga won the toss and sent Pakistan into bat in the first day-night international in Dubai on Friday.
The green shirts, having lost the two-test series against Sri Lanka 2-0, beefed up their batting for the five-match series with the return of Fakhar Zaman, Ahmed Shehzad, Shoaib Malik, and Mohammad Hafeez.
Fast bowler Mohammad Amir has been ruled out of the series due to a shin injury. Pakistan included fast bowlers Hasan Ali, Rumman Raees, and Junaid Khan in the XI.
Sri Lanka has twice been whitewashed in ODI series this year, first in South Africa and then at home against India. Its star performers in the test series victory against Pakistan Dimuth Karunaratne, Rangana Herath and Dilruwan Perera have already flown home.
The remaining matches will be held in Abu Dhabi (October, 16 and 18) and in Sharjah (October, 20 and 23).
Three Twenty20 internationals will follow the ODIs, the last in Lahore on October 29.
Pakistan: Sarfraz Ahmed (capt), Ahmed Shehzad, Fakhar Zaman, Mohammad Hafeez, Babar Azam, Shoaib Malik, Imad Wasim, Shahdab Khan, Hasan Ali, Rumman Raees, Junaid Khan
Sri Lanka: Upul Tharanga (capt), Dinesh Chandimal, Niroshan Dickwella, Lahiru Thirimanne, Kusal Mendis, Milinda Siriwardana, Thisara Perera, Lahiru Gamage, Suranga Lakmal, Akila Dananjaya, Jeffrey Vandersay
Sundaram Ravi (India) and Ahsan Raza (Pakistan) Tv umpire: Richard Kettleborough (England) ICC match referee: Andy Pycroft (Zimbabwey)