Shahid Afridi claimed 3-47 and Mohammad Yousuf hit 53 as Pakistan beat Sri Lanka to seal the series, and a place in October's ICC Champions Trophy.
The four-wicket one-day win means England also avoid having to qualify, while Sri Lanka play extra matches.
Sri Lanka were bowled out for 224 having been cruising at 93-1 after 22 overs after Chamara Kapugedera's 50.
Openers Shoaib Malik and Imran Farhat hit 46 each and Abdul Razzaq completed the win with a six in the 46th over.
The new Champions Trophy format guarantees places to the top six sides in the ICC rankings on 1 April.
England will not drop below Sri Lanka even if they lose their opening two games in India, giving them an extra fortnight off in September before a brutal winter programme.
Meanwhile, Sri Lanka will have to play in a qualification tournament with West Indies, Bangladesh and Zimbabwe.
Put into bat in the morning in Colombo, the hosts had started their innings well with Upul Tharanga (23) and Kapugedera sharing a 57-run opening stand.
"The boys have not played Murali much in the past but they have played him really well"
Razzaq made the first breakthrough when Tharanga slashed at a wide delivery to be caught behind.
But 18-year-old Kapugedera, a makeshift opener because of an injury crisis in the Sri Lanka camp, impressed with a maiden international fifty.
Kapugedera was one of two top order batsmen run out by Younis Khan when he was sent back late by Sangakkara having tried to pinch a quick single.
Younis also dismissed captain Mahela Jayawardene, who had been anchoring the middle order with 31 from 56 balls, with a direct hit from cover.
Tillakaratne Dilshan lifted the hosts past the 200-mark with an enterprising 44 from 46 balls before being bowled in the penultimate over while attempting an ambitious reverse sweep.
The Sinhalese Sports Club pitch eased during the second session and Malik gave Pakistan a flying start, hitting nine boundaries before driving a catch to cover.
Spinner Muttiah Muralitharan dismissed Malik, Younis (25) and Inzamam-ul-Haq (13) for his first wickets of the series but was uncharacteristically expensive as he finished with 3-58.
Captain Inzamam was pleased by Pakistan's play against Muralitharan throughout the series, with the first of two Tests starting on Sunday.
"The boys have not played Murali much in the past but they have played him really well." he said.
"Hopefully they will continue that in the Test series."
Sri Lanka's stand-in captain Mahela Jayawardene said: "We had a good start but lost the momentum when we lost wickets on a regular basis."