Sri Lanka won the toss and elected to bowl first, hoping to take advantage of the grass-covered pitch and conditions favourable to fast bowlers.
Pakistan handed Test debuts to four players: batters Tayyab Arif and Muhammad Taha, spin-bowling all-rounder Arafat Minhas and fast bowler Saqib Khan.
Openers Azan Awais and Tayyab Arif gave Pakistan a solid start, putting together an 86-run partnership for the first wicket.
Awais was dismissed for 30 by Milan Rathnayake, while Tayyab continued his aggressive approach against the Sri Lankan bowling attack.
Tayyab scored 57 off just 51 balls, hitting nine fours and a six, before Pakistan lost their second wicket at 90.
Following the early dismissals, Babar Azam steadied the innings alongside debutant Muhammad Taha. The pair built an important partnership to help Pakistan regain control.
Babar scored 50 off 58 deliveries, including seven boundaries, before being caught off Rathnayake at a total of 159.
After Babar's departure, Saud Shakeel joined Taha at the crease and added 68 runs for the fourth wicket.
Taha marked his Test debut with an impressive half-century, scoring 51 off 6 fours before being dismissed after the tea break at 227.
Pakistan suffered their fifth setback at 253 when Salman Ali Agha was dismissed for 16 runs.
Saud Shakeel and the remaining batters continued the innings as Pakistan moved to 281 for 5.
For Sri Lanka, Asitha Fernando has taken two wickets, while Dilshan Madushanka, Milan Rathnayake and Sonal Dinusha have claimed one wicket each.
Pakistan have fielded a relatively new-look side for the opening Test, with four players making their international Test debuts.
Sri Lanka, meanwhile, have left out experienced spinner Prabath Jayasuriya and opted for a four-man pace attack.
Speaking after the toss, Sri Lankan captain Kusal Mendis said the grass on the pitch could assist fast bowlers during the opening session, making the start of the match particularly important.
The two-match Test series is part of the ICC World Test Championship. Pakistan are currently ninth in the standings, while Sri Lanka occupy seventh place. Both sides will be looking to improve their positions through the series.
