Sri Lanka raced to their 171-run victory target in 31.5 overs during the afternoon with opener Malinda Warnapura scoring a brisk 54, Kumar Sangakkara an aggressive 46 and Mahela Jayawardene finishing off the game with an undefeated 37.
Having won the first test in Galle by 50 runs, Sri Lanka now have an unassailable 2-0 lead in the three-test series and can celebrate their first series win against Pakistan on home soil.
The run chase had been set up by bowlers Rangana Herath and Nuwan Kulasekara, the pair ripping through the Pakistan order after lunch as nine wickets fell for just 35 runs.
Spinner Herath claimed career-best figures of 5-99 and seamer Kulasekara finished with 4-37 as Pakistan were dismissed for 320.
A few hours earlier, Pakistan had seized control of the match when makeshift opener Fawad Alam (168) and skipper Younus Khan (82) compiled a 200-run partnership to put the tourists in a strong position on 285-1 shortly before lunch.
Pakistan's good position at that stage was remarkable considering their woeful batting on day one when they were bowled out for just 90, a record low against Sri Lanka.
However, a rash reverse sweep from Younus gave Sri Lanka's dispirited fielders a much-needed lift just before the break and ended a record second-wicket stand at the P. Sara Oval.
UNUSUAL PLOY
Sri Lanka skipper Kumar Sangakkara took the new ball straight after lunch and handed it to his slow bowlers, an unusual ploy that worked beautifully.
Mohammad Yousuf (6) was the first to go as he lost his balance and was trapped lbw on his back leg -- the third time in four innings he has been dismissed by Herath this series.
With Yousuf gone, Sangakkara changed tactics and introduced Kulasekara, his premier fast bowler, who went on to compile match figures of 8-58 from his 28.4 overs.
Kulasekara swung the ball sharply into the right-handers and picked up four lbw decisions, the first of which was the dangerous Misbah-ul-Haq for three.
Sri Lanka were soon back in command when Alam was caught at short leg, ending a 384-minute debut vigil that spanned 259 balls and included 15 boundaries and one six.
The 23-year-old is the first batsmen from his country to score a century on his debut in an overseas test and also owns the highest score by a Pakistan batsman in Sri Lanka, overtaking the 155 made by Salim Malik in 1997.
The innings then descended into freefall with Shoaib Malik (6) bowled by an arm ball, Kamran Akmal (3) trapped lbw by a Kulasekara inswinger and the rest of the tail folding with barely a fight.
Sri Lanka's openers seized early momentum with Tharanga Paranavitana (17) and Warnapura adding 60 in just 10 overs.
Off-spinner Saeed Ajmal eventually bowled Paranavitana and Warnapura was caught behind off seamer Abdur Rauf, but Sangakkara and Jayawardene ensured Sri Lanka a clinical victory.
