De Zorzi survived several reviews in a charmed existence at the crease but provided resistance as the tourists struggled to deal with Pakistan's spin attack on a slowing surface and with cracks beginning to show at the Gaddafi Stadium.
He will resume with Senuran Muthusamy, not out on six, at the start of the day three on Tuesday after Muthusamy's bowling caused a sudden collapse in Pakistan's innings earlier on Monday.
The home team were in a commanding position at 5-313 overnight, with Mohammad Rizwan 62 not out and Salman Ali Agha unbeaten on 52, and looked to be heading to an imposing total before the left-arm spinner took three wickets in four balls in the 12th over of the morning.
Pakistan collapsed from 5-362 to 378 all out as Muthusamy finished with Test best figures of 6-117.
Rizwan (75) began the procession as he was deceived by extra bounce and feathered the ball through to wicketkeeper Kyle Verreynne, who took a sharp catch to end a 163-run partnership for the sixth wicket.
Salman was 84 not out and would have been watching in increasing horror as a procession of batting partners quickly departed thereafter.
He had moved to 93 when the last batsman came out and was caught at long on chasing the runs needed to get to his century, falling seven short as Imam Ul-Haq had done on the opening day.
South Africa lost their first two wickets for 80 runs, but Ryan Rickelton and De Zorzi put on 94 for the third wicket before Rickelton was dismissed for 71 by a reflex catch from Babar Azam off Salman's bowling.
But from 3-174, the tourists found it increasingly difficult to dominate Pakistan's spin attack and lost three more wickets cheaply as Noman Ali took 4-85 and Sajid Khan had the dangerous Dewald Brevis caught first ball.
"We need to get them out as early as possible, and a 120-run lead would help us win this Test," said Noman.
"This pitch will further help spinners in the coming days, so it's good for us."
The Test is the first of the two-match series, with the second in Rawalpindi starting on October 20.
