Sri Lanka pace bowler Vishwa Fernando took two wickets in three balls to leave Pakistan struggling at 72-3 on the opening day of the second Test in Karachi on Thursday.
The left-armer removed opener Shan Masood for five and skipper Azhar Ali without scoring in the seventh over after Pakistan won the toss and batted on a greenish-brown National Stadium pitch.
Fernando's new-ball partner Lahiru Kumara dismissed first Test centurion Abid Ali for 38 to end a third-wicket partnership of 55 which had lifted Pakistan from a precarious 10-2.
At the break, Babar Azam was not out 27 and Asad Shafiq on one.
Fernando gave Sri Lanka an early breakthrough as he angled one from Masood to hit his off stump before clean bowling skipper Azhar with a full-length delivery.
That left Azhar without a fifty in 13 innings, including nine scores of under 10.
Pakistan brought in leg-spinner Yasir Shah for paceman Usman Shinwari who has typhoid while left-arm spinner Lasith Embuldeniya came in for unfit medium -pacer Kasun Rajitha in Sri Lanka's only change.
The two-match series is the first in Pakistan since a militant attack on the Sri Lankan team bus killed eight people in March 2009, leading to the suspension of international cricket in the country as foreign sides refused to visit over security fears.
The rain-ravaged first Test ended in a draw.
Sri Lanka's Vishwa Fernando bowls on the way to taking two Pakistan wickets in three balls before lunch on the first day of the second Test in Karachi
Pakistan skipper Azhar Ali loses his off stump to Vishwa Fernando