KARACHI, Oct 31: Danish Kaneria triggered a Sri Lankan collapse in the final session to leave Pakistan poised for victory in the decisive second Test here at the National Stadium on Sunday.

Sri Lanka, trailing by 270 runs on the first innings, lost four crucial wickets in the last hour of the fourth day to finish at 361 for seven in their second innings with leg-spinner Kaneria taking six for 102 in lion-hearted 45 overs on a day when the pendulum generally swung in Sri Lanka's favour for a better part of the day.

A patient century by Kumar Sangakkara, who shared the day's spotlight with Kaneria, had kept Pakistan struggling till the final session of the day. The 27-year-old Kandy-born law student went to score 136 - his seventh century in 44 Tests and third this year - in five and three quarter hours of determined batsmanship.

Sangakkara brought up his second century in three Tests against Pakistan in 274 minutes by striking Abdul Razzaq twice through the point and cover region for successive boundaries. Overall, his 251-ball innings was studded with 20 fours and one six, hoisted over long-off fence off Kaneria.

Sangakkara had almost ensured his side a safe passage at 295 for three at the tea interval after the tourists had lost a wicket each in the first two sessions, those of Sanath Jayasuriya (107) and Mahela Jayawardene (32), both to the persevering Kaneria.

But Pakistan, who must win here to prevent a hat trick of Sri Lankan series victories in this country, hit back with vengeance as four wickets went for 27 runs in 62 balls.

Kaneria dismissed Thilan Samaraweera, Jehan Mubarak and Romesh Kaluwitharana in a splendid spell that saw him bagging three wickets for six runs in 26 deliveries.

With a lead of just 91 runs, Sri Lanka face an uphill battle to escape defeat on the final day of the two-match series on a pitch still playing true.

Chaminda Vaas (2) and Farveez Maharoof (0), both with some batting credentials, confront a challenging task on Monday to prevent Pakistan from squaring the series.

The second new ball, taken first thing after tea, changed Pakistan's luck. Rana Naveedul Hasan, the debutant who had been unlucky on several occasions, was deservingly rewarded for his labour when he forced the well-set Sangakkara to edge a catch to wicket-keeper Kamran Akmal.

Sangakarra, perhaps infuriated at his dismissal, tossed his bat in disgust before heading for the pavilion. Normally a free-scoring batsman, until that moment of sudden rashness, had restrained himself from trying anything foolish.

But his act could tempt Jeff Crowe, the ICC match referee from New Zealand, to take some sort of punitive measure against the Sri Lankan.

"I was very disappointed at getting out to such a loose shot that forced me to behave like that," Sangakkara said of his dismissal afterwards.

"The entire team had shown a lot of character but I should have carried on. But unfortunately, since I got out we lost a couple of more wickets very quickly to leave us in a disappointing situation.

"A hundred is always good. But it's nice once in a while to get one under pressure after conceding such a big lead. Overall, it was one of my better knocks because I had to work for it."

Sangakkara complimented Kaneria's excellent contribution. "I thought he bowled brilliantly on a pitch that is behaving normally. He is definitely a good bowler."

Jayasuriya, resuming the day on 96 in a total of 134 for one, perished after adding 53 with Sangakkara when he top-edged a sweep and was caught by Shoaib Malik, running in from deep backward square-leg.

The seasoned campaigner's fourth century against Pakistan, his second in the current series following a record-breaking 253 at Faisalabad, took his series aggregate to 424 - the most for Sri Lanka in Pakistan eclipsing Sidath Wettimuny's 316 runs in the inaugural series between the two countries.

Jayasuriya's 107 off 129 balls (which contained 14 fours and one six in a stay of two and a half hours) took his tally of runs in the current year to 1130 in 11 Tests. Sangakkarra also raced past the 1,000-run mark in 2004 and joined a select group of seven players who had achieved the 'double' in both forms of the game.

Sri Lanka batted dourly in the afternoon session of play, scoring only 61 in 29 overs after having put on exactly 100 in the same number of overs in the morning with a couple of useful partnerships.

Jayasuriya and Sangakkara added 53 for the second wicket. Then Jayawardene was involved in a third-wicket partnership of 83 with Sangakkara, who in turn shared yet another fruitful partnership of 80 for the fourth wicket with the obdurate Samaraweera (22 off 168 balls).

Watched by a crowd, that had swelled to over 4,000 with a majority invited free of charge, it was a dull proceeding in the post-lunch period during the only casualty was Jayawardene, easily caught by Yasir Hameed via bat/pad at short-leg as the Sri Lankan vice-captain prodded forward hesitantly.

Kaneria, who bowled a marathon unbroken spell of 27 overs from the Pavilion End on either side of lunch and tea, richly deserved his sixth five-wicket haul in his 20th Test when he bamboozled Mubarak, the Washington-born left-hander, with a sharp spinning delivery that caught the inside edge of his bat and carried to Imran Farhat at leg-slip.

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