At tea, skipper Babar Azam was unbeaten on 77 with Fawad Alam on 42 not out.
Proteas are playing a Test match at the Pindi Cricket Stadium after 24 years.
No changes have been made to Pakistan's 17-player squad from the first Test in Karachi.
RAWALPINDI: Skipper Babar Azam and Fawad Alam rescued Pakistan from early shocks and took the score to 145-3 at tea on the opening day of the second Test in Rawalpindi on Thursday.
Play could not be resumed after tea due to rain and a wet outfield, with skipper Babar Azam 77 not out, and Fawad Alam undefeated with 42.
Earlier, Spinner Keshav Maharaj (2-51) and pacer Anrich Nortje (1-30) had left Pakistan struggling on 63-3 at lunch but Azam and Alam added 123 for the unbroken fourth wicket stand to steady the innings.
Azam, who managed just seven and 30 in the first Test, returned to his stylish best, having so far punched 12 boundaries in his 16th Test half-century.
Alam, who scored a fighting hundred in the first Test, was steady with five hits to the fence.
Earlier, Pakistan, who won the toss and batted, reached 21 without loss before throwing away three wickets for one run in the space of 23 balls.
Maharaj, brought into the attack in just the ninth over, had opener Imran Butt caught behind for 15 and then trapped senior batsman Azhar Ali leg-before for nought in his next over.
Nortje then produced a sharp rising delivery to Abid Ali, (six) whose fended push was caught smartly at short-leg by Aiden Markram.
Pakistan lead the two-match series 1-0 after winning the first Test in Karachi by seven wickets.
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