Fawad Alam's century on debut helped Pakistan in their recovery on day two of the second Test against Sri Lanka in Colombo.

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Pakistan had started the day staring down the barrel, but Umar Gul gave their fightback impetus with a three-wicket haul in the morning session.

Ably assisted by off spinner Saeed Ajmal, Gul helped restrict Sri Lanka's first innings lead to just 150 as they were bowled out for 240.

Alam and opening partner Khurram Manzoor then gave the visitors a sound start to their second innings with an 85-run stand for the first wicket - Pakistan's best opening partnership of the series so far.

At close, Pakistan had battled to 178 for one, an overall lead of 28 with Younus Khan batting on 35 and Alam on 102.

It's all about numbers

The day began on a bizarre note with Pakistan briefly losing the ball in the morning which delayed the start of play.

The visitors had left the ball lying on the turf while setting the field and a member of the ground staff had removed it.

But the ball was soon traced after a frantic, but brief, search which also involved the third umpire.

Pakistan, who were bowled out for just 90 runs in the first innings, urgently required quick wickets and were aided almost immediately by the run out of Thilan Samaraweera.

The middle-order batsman, who began with a nicely driven boundary straight past the bowler, struck another delivery firmly to mid-off and set off for a single.

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However, Mohammad Aamer pounced on the ball and rattled the stumps at the non-striker's end with a direct throw, catching Samaraweera well short of safety.

The introduction of Gul then immediately put Sri Lanka's batsmen under pressure by generating reverse swing.

Gul soon removed Kumar Sangakkara with one that pitched well outside off stump and veered sharply in, beating the batsman's defence and pegging back off stump.

Sangakkara had added only six runs to his overnight 81 and his departure brought Tillakaratne Dilshan and Angelo Mathews to the crease, Sri Lanka's last recognised batting pair.

Dilshan began in customary energetic fashion and initially scored better than a run a ball. He clubbed Ajmal for a couple of boundaries and had progressed to 20 when he was undone by a poor caught-behind decision from umpire Daryl Harper.

Mathews, who was dropped on four by Manzoor at slip, attempted to shield the tail, but Gul struck off consecutive deliveries in one over to remove Nuwan Kulasekara and Rangana Herath.

Five wickets had fallen in the first session as Sri Lanka seemed to have inherited Pakistan's batting frailties.

And the end came quickly for the hosts with Abdur Rauf getting rid of Thilan Thushara soon after the lunch interval before Mathews fell to Ajmal for 27.

Sri Lanka were all out for 240, Gul finishing with four wickets for 43, while Ajmal had figures of four for 87 from 31 overs.

Sri Lanka, who had the opportunity to bat Pakistan out of the Test and seal the series, were still in command at that stage, but the home side lost their grip as Manzoor and Alam took up the task of wiping out the deficit.

Manzoor began with an edged boundary, but then settled down to turn out a far more composed innings.

Kulasekara and Thushara managed some movement with the new ball, but the batsmen weathered the storm.

Herath eventually broke the partnership although Dilshan too played his part nicely. Manzoor rocked back to cut a short pitched delivery and bottom-edged to Dilshan, who completed a sharp catch.

Alam was then joined by Younus and the two erased the deficit even as the 23-year-old Alam closed in on a century.

He became Pakistan's first batsman to score a century on debut away from home, getting to the mark with a six off Herath, clubbed through midwicket, and a couple of runs through third man off the very next delivery.

Alam has so far added 93 runs for the second wicket with Younus.