Sri Lanka's players congratulate Pakistan's Imam-ul-Haq (centre) and Agha Salman (third right) at the Galle International Cricket Stadium in Galle on Thursday. AFP

Opening batsman Imam-ul-Haq hit an unbeaten 50 to steer Pakistan home in their tricky chase of 131 against Sri Lanka and win the first Test by four wickets on Thursday.

The tourists started the final day on 48-3 and lost three more wickets, including skipper Babar Azam for 24 off Prabath Jayasuriya, before they achieved the target in the first session.

Haq started the day on 25 and remained calm with Azam and then left-handed partner Saud Shakeel, who made a brisk 30 after his unbeaten 208 in Pakistan's first innings.

Left-arm spinner Jayasuriya took four wickets including two on the evening of day four to give the hosts a glimmer of hope, but Haq stood firm.

Azam came out roaring as he hit a boundary off the first ball of the day and looked fluent in his 28-ball stay before being trapped lbw by Jayasuriya.

Shakeel took on the bowlers as well but off- spinner Ramesh Mendis got him caught behind.

Haq reached his eighth Test fifty before Jayasuriya took another wicket and Agha Salman came out to hit the winning six.

Shakeel stood out for his maiden Test double century in Pakistan's 461 all out and a handy first-innings lead of 149 in the rain-hit match.

Pakistan spinners Noman Ali and Abrar Ahmed made it count with three wickets each on Wednesday to help bowl out Sri Lanka for 279 despite Dhananjaya de Silva's stubborn 82.

De Silva made 122 in Sri Lanka's first innings of 312 after the hosts elected to bat first but soon Pakistan took control.

Pakistan pace spearhead Shaheen Shah Afridi took a match haul of five wickets on his return to Tests since a knee injury put him out of action a year ago at the same venue.

The second match of the two-Test series starts Monday in Colombo.