A trademark second innings collapse Sunday saw Pakistan bowled out for a paltry 180 in Galle giving the hosts a chance to win the match.
Sri Lanka knocked off the 99-run target despite bad light and intermittent rain to take a 1-0 lead in the two-Test series.
"It was disappointing to see Pakistan lose a Test which was heading for a draw and after scoring 451," former captain Rashid Latif told AFP.
Younis Khan led the charge in the first innings with a brilliant 177 but Sri Lankan spinner Rangana Herath exploited the last-day pitch with figures of 6-48 to destroy Pakistan's batting.
In contrast Sri Lanka notched up 533 for nine declared in the first innings with Kumar Sangakkara hitting a magnificent 221, blunting Pakistani spinners Saeed Ajmal and Abdur Rehman.
Latif said neither Rehman nor Ajmal had lived up to expectations.
"Considering Pakistan's batting frailties, Ajmal and Rehman didn't bowl well (to compensate) and that was the cause of defeat," said Latif, adding the defeat did not augur well for Misbahul Haq's captaincy.
"I can see Shahid Afridi as captain in the 2015 World Cup if Pakistan lose the Test and one-day series in Sri Lanka," said Latif.
The second Test starts in Colombo on Thursday and is followed by a three-match one-day series.
Latif also criticised Pakistan's policy of employing too many coaches.
"No matter how many coaches you bring, it cannot improve. All the coaches are job seekers," said Latif, singling out spin coach Mushtaq Ahmed.
In May this year the Pakistan Cricket Board appointed former paceman Waqar Younis as head coach and former Zimbabwe opener Grant Flower batting coach.
Another former captain, Mohammad Yousuf, criticised the team's go-slow batting which allowed the Sri Lankan spinners to attack.
"I did not expect such a batting capitulation but it all boils down to the defensive strategy of the captain and that has let the team down," said Yousuf.
Pakistani middle-order batsman Azhar Ali took 151 balls for his 41 runs while opener Ahmed Shehzad scored 16 off 74.
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