A dominant all-round performance by Mohammad Hafeez steered Pakistan to a six-wicket victory 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.
Hafeez, later named man of the match, said he had put aside the scrutiny of his bowling action.
"I have definitely put that aside and tried to concentrate on what is in my hands," he said. "This series is important for us and we wanted to have a good start.
"I am glad I could contribute to this win and hope I can continue in the same way in the remaining matches.
"There was no pressure on me. I was given the green signal from the management to play aggressively and the plan worked."
Sri Lankan captain Angelo Mathews admitted Pakistan outplayed his side.
"We did not play our best cricket," he said. "We just could not put up a good score and also could not pick up wickets at crucial stages.
"Hopefully we can comeback in the next few games. We need to prepare well mentally."
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 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.
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.
Pakistan beat Sri Lanka by six wickets in the first one-day international at Dambulla on Saturday to take a 1-0 lead in the five-match series.
All-rounder Hafeez starred for the tourists taking four for 41 and then blasting 103 off 95 balls cracking 10 fours and four sixes.
Pakistan chased down the target of 256 with nearly five overs to spare making 259-4 in 45.2 overs with Malik remaining unbeaten on 55 off 45 balls hammering four boundaries and two sixes, including the winning hit.
Openers Azhar (21) and Shehzad (29) gave Pakistan a steady start with a stand of 47 before the advent of Hafeez who shared in partnerships of 58 for the third wicket with Azzam (58) and Malik (75) for the fourth during his belligerent knock.
Malik steps out and lofts Dilshan for a six over long-off to complete his half century and seal a six-wicket victory for Pakistan making 259-4 in 45.2 overs chasing a target of 256.
Hafeez throws his wicket away after completing his century. Pak 198-4, 35.5 overs.
Mohammad Hafeez c & b Thisara Perera 103 (95b 10x4 4x6)
Hafeez cracks Thisara to the point boundary to complete his 10th ODI century.
Hafeez moves to 95 with lofting Dilshan for his fourth six. Pak 185-3, 34 overs.
Hafeez completes his 26th ODI half century in style coming down the track and slamming for a six. Pak 134-3, 27 overs.
Dilshan strikes trapping Azzam leg before. Pak 123-3, 25.2 overs.
Babar Azam lbw b Dilshan 25 (30b 3x4 0x6)
Lakmal strikes with the first ball of a new spell as Shehzad gets out fishing. Pak 65-2, 14.1 overs.
Ahmed Shehzad c Chandimal b Lakmal 29 (39b 4x4 0x6)
Hafeez cracks Mathews through the covers for a boundary to open his account. Pak 51-1, 10 overs.
Chandimal standing up close combines with his skipper to get the first breakthrough for Lanka. Pak 47-1, 9.2 overs.
Azhar Ali c Chandimal b Mathews 21 (29b 3x4 0x6)
Azhar flicks Malinga to long leg for the boundary of the innings while Shehzad pulls one to the midwicket fence. Pak 16-0, 3 overs.
Sri Lanka innings
Sri Lanka put into bat have made a competitive 255-8 thanks to a superb unbeaten half century from Dinesh Chandimal (65).
Dilshan made a sedate 38 while Hafeez struck at regular intervals to claim four for 41.
Skipper Mathews (38) shared in a crucial stand of 82 for the fifth wicket with Chandimal who cracked five boundaries and a six.
Debutant Milinda Siriwardana weighed in with a cameo of 22 as Sri Lanka plundered 63 in the last 10 overs.
Double strike by Rahat as Prasanna departs for a golden duck. SL 245-8, 48.5 overs.
Seekkuge Prasanna c Mohammad Hafeez b Rahat Ali 0 (1b 0x4 0x6)
Siriwardana perishes in the search for quick runs. SL 244-7, 48.2 overs.
Milinda Siriwardana c Mohammad Rizwan b Rahat Ali 22 (21b 2x4 1x6)
Hafeez claims his fourth as Thisara steers straight to slip. SL 204-6, 43 overs.
Thisara Perera c Mohammad Rizwan b Mohammad Hafeez 1 (3b 0x4 0x6)
Shah gets a crucial breakthrough as Mathews tries to hit against the spin only to miscue it to end a breezy stand with Chandimal. SL 200-5, 41.5 overs.
Angelo Mathews c Babar Azam b Yasir Shah 38 (54b 5x4 0x6)
Hafeez claims his third wicket as Dilshan plays all over a Hafeez delivery. SL 118-4, 26.1 overs.
TM Dilshan b Mohammad Hafeez 38 (65b 2x4 0x6)
Hafeez has struck again beating another left-hander with his flight and spin. SL 111-3 23.4 overs.
Upul Tharanga st Sarfraz Ahmed b Mohammad Hafeez 20 (27b 2x4 0x6)
Tharanga opens his account with a streaky boundary off Anwar. SL 88-2, 17 overs.
Anwar strikes in the first over after drinks breaks as Thirimanne edges one behind. SL 82-2, 16.3 overs.
Lahiru Thirimanne c Sarfraz Ahmed b Anwar Ali 23 (23b 2x4 1x6)
Thirimanne hits the first six of the match sweeping Hafeez over midwicket. SL 71-1, 15 overs.
Thirimanne gets going cracking Hafeez to the third man fence. SL 54-1, 11 overs.
Spin does the trick for Pakistan with Kusal edging Hafeez to slip. SL 44-1. 8.3 overs.
Kusal Perera c Mohammad Rizwan b Mohammad Hafeez 26 (35b 4x4 0x6)
Kusal cracks a couple of boundaries off Rahat. SL 44-0, 8 overs.
Kusal gets going cracking Anwar through the covers for a boundary while Dilshan slashes one to third man. SL35-0, 7 overs.
Dilshan survives after being caught behind off a no-ball from Irfan in the third over. SL 10-0.
Pakistan have won the toss and put Sri Lana into bat in the first one-day international at Dambulla on Saturday.
Sri Lanka has handed a debut to left arm spinning allrounder Milinda Siriwardana while giant fast bowler Mohammed Irfan returns for Pakistan after an injury lay-off.
Sri Lanka: MDKJ Perera, TM Dilshan, HDRL Thirimanne, WU Tharanga, LD Chandimal, AD Mathews, TAM Siriwardana, NLTC Perera, S Prasanna, RAS Lakmal, SL Malinga
Pakistan: Azhar Ali, Ahmed Shehzad, Mohammad Hafeez, Babar Azam, Shoaib Malik, Mohammad Rizwan, Sarfraz Ahmed, Anwar Ali, Yasir Shah, Rahat Ali, Mohammad Irfan