Hasan Ali's five wickets gave Pakistan a first-innings lead over South Africa in the second Test but the hosts lost early wickets as they looked to build on their advantage.
George Linde took three wickets and Keshav Maharaj two as the two teams wrestled for advantage on the third day on Saturday.
Pakistan closed on 129-6 with an overall lead of 200 on a tacky Rawalpindi Cricket Stadium pitch which has cracks to help slow bowlers.
Linde (3-12) and Maharaj (2-74) rattled Pakistan's top order before Faheem Ashraf (29) and Mohammad Rizwan (28 not out) saved Pakistan's blushes during their 52-run sixth wicket stand.
Linde managed to remove Ashraf, caught in the covers, before bad light ended play.
The day could have ended in South Africa's control had Ashraf and Rizwan not been dropped off the two spinners.
Ashraf was yet to get off the mark when Dean Elgar grassed an edge off Linde in slips while Rizwan was four when Rassie van der Dussen let off a sharp chance off Maharaj.
Pakistan would hope another 50 runs on Day 4 could win them the match and the series, having won the first Test in Karachi by seven wickets.
"Even chasing 200 won't be easy on this pitch," Hassan said. "We will try to get to 240 to 250 and with our spinners it won't be easy."
The highest target chased in the previous ten Tests at this venue is 220 which Sri Lanka chased to beat Pakistan by two wickets in 2000.
"Obviously we have to win this Test to level the series," Linde said. "I think anything under 300, we will take that for a chase."
Earlier, Hasan's 5-54 – his second five-wicket haul in Tests – restricted South Africa's first innings to 201, giving the home team a lead of 71. Pakistan had made 272 in their first innings.
Stumps in Rawalpindi with the match hanging in the balance.
— ICC (@ICC) February 6, 2021
12 wickets fell on day three with @TheRealPCB 129/6 at the close.#PAKvSA | https://t.co/dHR9CvSfxt pic.twitter.com/JDLDBRbCsY
