Sri Lanka got a 99-run target despite bad light and intermittent rain to take a 1-0 lead in the two-Test series.
A trademark second innings collapse on Sunday meant Pakistan were bowled out for a paltry 180 in Galle after the match looked certain to end in a draw.
Former skipper and wicket keeper Rashid Latif told a news agency that “It was disappointing to see Pakistan lose a Test which was heading for a draw and after scoring 451.
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.
Latif said neither Rehman nor Ajmal had lived up to expectations.
The former skipper said the defeat did not augur well for Misbah-ul-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,” Latif said.
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.