Dhammika Prasad chipped in with two wickets as the hosts bowled Pakistan out for 102 and then surpassed the Duckworth-Lewis target of 101 in the 19th over of a one-sided game in Dambulla.
An hour-long rain interruption after Pakistan had slumped to 81-8 in the 26th over of the first session forced the umpires to reduce the game to 48-overs-a-side.
Sri Lanka galloped home in style to build on the 2-0 sweep in the preceding Test series and left Pakistan searching for answers ahead of the World Cup less than six months away.
Opener Upul Tharanga and Kumar Sangakkara fell cheaply before Mahela Jayawardene (26) and Dilshan put on a 41-run stand for the third wicket.
Dilshan cut Shahid Afridi to the fence to bring up his half-century and also seal his team's easy win.
Fawad Alam top-scored for Pakistan with an unbeaten 38, but eight batsmen failed to reach double figures as the tourists crumbled in 32.1 overs after electing to bat on the slow wicket.
It was Pakistan's lowest one-day total on Sri Lankan soil, falling below the 116 they made against New Zealand at the same venue in 2003.
Pakistan captain Misbahul Haq said it was not a difficult wicket to bat on.
"There was a bit of tennis-ball bounce, but we should still have scored about 240-250 runs," Misbah said. "We lost too many wickets early and could not get a decent total."
Misbah hoped Pakistan will perform better in their next Test and one-day series against Australia in the United Arab Emirates in October.
"That is a really important series and we need to find the right combination ahead of the World Cup," he said.
Sri Lanka's captain Angelo Mathews said his team showed character to bounce back after losing the first match of the series in Hambantota.
"We had to pull up our socks after that loss and we did that quite well," he said. "We gave Thisara (Perera) more opportunities in the series and he proved himself with both bat and ball."
Sri Lanka next host England for a seven-match one-day series starting in November.
Pakistan never recovered after losing opener Sharjeel Khan in the third over, caught at second slip off Prasad.
Prasad, who replaced the off-form Nuwan Kulasekara, then had the other opener, Ahmed Shehzad, caught at mid-on to make it 14-2.
The third wicket fell at the same total when Lasith Malinga had Mohammad Hafeez leg-before for one as the TV umpire upheld the decision following a review by the batsman.
It soon became 55-5 by the 19th over when Misbah was run out for 18 by a direct throw from Dilshan and Umar Akmal holed out off Perera for seven.
The low total ruined any hopes Pakistan had of snatching a dramatic win with the help of their spin spearhead Saeed Ajmal, who was back after missing the previous two matches to have his bowling action tested.
Ajmal had flown to Brisbane, Australia, for the tests after his action was reported by the umpires during the Test series. He is allowed to play on until the results of the tests are made known.
Ajmal picked up the wicket of Jayawardene, caught in the slips, but Sri Lanka were only one run away from victory at that stage.
The World Cup is to be played in Australia and New Zealand in February-March next year.
COMMENTS (11)
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One of the Akmal Brothers has to be in the team. "Captain" Misbah said upon losing test matches to Sri Lanka that they were not ashamed of losing to Sri Lanka because they are a good team. PCB thugs should arrange this team's matches with Kenya, Holland and Bhutan only so they feel ashamed after losing to them
PRIVATIZE, PRIVATIZE, PRIVATIZE! Disband the PCB and send all the players home. Send Shahryar Khan and Najam Sethi home. Convert the PCB HQ building into a public library or an orphanage. Hold Ejaz Butt accountable et al. THE SOONER THE BETTER. Salams
@Iqbal Hadi Zaidi: It is a cricket match play it for the spirit of game. You win some ,lose some.Enjoy the game Sri Lankans should be admired for the performance and Pak team does not need to be castigated. Looks like diplomat is most like a puppet king who thinks it is a war and returning players should be .......You need to stay in Middle East Must have lost some frontal lobe neurons Boys coming back you have nothing to be ashamed of ,you did your best, next time it will work, welcome back. Kalwant Sing being a gentleman is too kind to diplomat.
Why we cry, SL played well and won, we not played well We should enjoy the game, any body play well, good to watch...
@Iqbal Hadi Zaidi: Diplomate Sahib it is game not Indo/Pak war some time very good teams perform very poorly and very good players fail to score even a single run is it fair to send then to jail, you tell the weaknesses of the team and advise them to look into these .
good style fawad alam playing with eyes closed-I think SERIOUS problem is in PCB not in the team.
WOW! our team is giving what a performance under the corps of coaches and now one more coach required to tell how over to come repeated sorrows.
Pakistan coach and PCB chairman should be changed!! Both of them failed I promises of cricket glory rivival.
I am Pakistani and wish Pakistan to win but the fact remains that we cannot play against strong teams and official records can prove my point of view but what I condemn most is the tall claims of our captains and selectors alike. I have written in good olden days that when team returns after humiliating defeat then the team be jailed because they are welcomed by President of Pakistan when return victorious. Cant we maintain equilibrium or want to stick to imbalance? Iqbal Hadi Zaidi / Former Diplomat / Kuwait / Mobile 00965-66229897 / zaidiformerdiplomat@hotmail.com
They are all spent forces. Pity is that after every three or four matches one dead log reappear. After this humiliating defeat we will see Taufiq Umar, Kamran Akmal, Yasir Hameed and someone even older back in team. Its a pack of dead woods. As long as new blood is not tested, the team remain a third class performer: winning every 1 out of 4 matches.
If you keep on ignoring players from Karachi this is what is going to happen. Umar Akmal was selected nobody knows why. Is it some kind of Hardees that one Akmal has to be in the side. Sarfaraz bated so well being the top scorer and he was sent back so was Asad Shafiq now only Fawad Alam if their and what maximum can he do,