A dominant all-round performance by Mohammad Hafeez steered Pakistan to a six-wicket win over Sri Lanka in the first one-day international in Dambulla on Saturday.
The off-spinner shrugged off concerns about his bowling action to grab four wickets as Pakistan, electing to field after winning the toss, kept Sri Lanka down to 255-8 in 50 overs.
Hafeez then hammered a stroke-filled 103 to lead the tourists past the target in 45.2 overs, giving them the lead in the five-match series.
Ninth-ranked Pakistan need to win the series to stay in contention for a place in the eight-nation Champions Trophy in England in 2017.
Sri Lanka, currently ranked fifth, are assured of taking part in the tournament.
Hafeez, who was reported for a suspect action during the preceding Test series and underwent tests in Chennai last week, took the field only because he is allowed to play till the results are declared.
The 34-year-old seized the opportunity to finish with his best one-day figures of four for 41 and to restrict Sri Lanka in good batting conditions.
Hafeez returned with the bat to strike 10 boundaries and four sixes in his 10th one-day century — the last four all coming against Sri Lanka.
Pakistan lost captain Azhar Ali and opening partner Ahmed Shehzad by the 15th over with the score at 65, before Hafeez settled in to fashion a rescue.
He put on 58 for the third wicket with Babar Azam (25) and 75 for the fourth with Shoaib Malik, who ended the match with a six off Tillakaratne Dilshan to move to 55 not out.
Hafeez reached his century in the 36th over with a four off Thisara Perera, but fell two balls later when he gave the same bowler a tame return catch.
Earlier, Dinesh Chandimal top-scored with an unbeaten 65 off 68 balls as the Sri Lankans struggled to come to terms with the accurate Pakistani bowling.
Chandimal put on 82 for the fifth wicket with skipper Angelo Mathews (38) and 40 for the seventh with debutant Milinda Siriwardana (22) after the first four batsmen had fallen for 118 by the 27th over.
Dilshan made 38 after being caught off a Mohammad Irfan no-ball when he was on two.
Seamer Rahat Ali took two wickets in the 49th over as Sri Lanka scored 56 runs in the last nine overs.
Pakistan had won the Test series 2-1 with a seven-wicket win in the final Test in Pallekele on Tuesday.
The second one-dayer will be played there on Wednesday.