Pakistan resumed the day on 71 for two, needing just 97 runs with eight wickets remaining to win the opener of the three-match series, but wickets tumbled from early in the morning session and the tourists were bowled out for 117 in less than 45 overs.
Left-arm spinner Rangana Herath, who was rushed into the contest from English league cricket after an injury to Muttiah Muralitharan, sparked the collapse with the wickets of Mohammad Yousuf (12) and Salam Butt (28).
Herath was Pakistan's chief tormentor, showing plenty of guile to claim impressive figures of 4-15 from 11.3 overs.
Yousuf, Pakistan's first-innings top scorer with 112, was the first man to go when he was trapped lbw with a well-disguised arm ball and Butt self-destructed with a wild slog-sweep that was caught at deep square leg.
Left-arm fast bowler Thilan Thushara, a controversial pick ahead of veteran Chaminda Vaas, vindicated his selection when he had former captain Shoaib Malik caught behind for a duck to leave Pakistan in disarray on 72-5.
Thushara, getting the ball to swing both ways, followed up with an inswinger to trap wicketkeeper Kamran Akmal lbw for six.
Sri Lanka keeper Tillakaratne Dilshan then seized on some clumsy calling to run out Misbah-ul-Haq for six shortly after an appeal for leg before was turned down.
Spinner Ajantha Mendis made an instant impact, bowling Umar Gul for nine with a fizzing leg-cutter.
Abdur Rauf and Mohammad Aamer threatened to stall the home side's victory charge with a partnership of 15 for the ninth wicket, but Herath deceived the latter with an arm ball soon after being called back for a second spell.
Herath then wrapped up victory just before the scheduled lunch break when he got Rauf to edge to Jayawardene at slip.
Mendis finished with 2-27 from 10 overs and Thushara chipped in with 2-21 from 12 overs.
