Bosch, batting at number nine, enabled South Africa to take a 90-run first innings lead –- and the bowlers made it count by taking three wickets before Pakistan could wipe out the deficit.
Pakistan finished the day on 88 for three –- still two runs behind.
South Africa would qualify for next year's World Test Championship final for the first time with a victory in either match of this two-Test series.
The contest was evenly poised when opening batsman Aiden Markram was eighth man out for 89 with South Africa on 213 for eight -– just two runs ahead of Pakistan's first innings total of 211.
Four South African wickets had fallen for 35 runs either side of lunch, with Naseem Shah taking three in a fiery spell, and it seemed probable the sides would start the second innings almost on level terms.
But Bosch, who has a first-class batting average above 40, batted with freedom and a wide variety of strokes as he shared stands of 41 with Kagiso Rabada (13) and 47 with Dane Paterson (12) to turn a narrow lead into a substantial one.
Bosch hit 15 fours in a 93-ball innings.
"It was a huge momentum shift and it was probably worth more than a hundred," said Markram, who captained Bosch and Rabada when South Africa won the Under-19 World Cup in Dubai in 2014.
It was the continuation of a remarkable debut for Bosch, 30, who took four for 63 in the first innings and was clocked at 147kmh, the fastest of any bowler in the match.
Bosch, whose Test cricketer father Tertius died when Corbin was five years old, was low on the list of potential Test fast bowlers at the start of the season.
But a lengthy list of injuries to bigger-name players, as well as good recent form, opened the door for him.
"He’s a really talented guy and in the last few years he's really put his head down and worked to get his opportunity," said Markram.
Bosch shared the new ball with Kagiso Rabada at the start of Pakistan's second innings but did not take a wicket and left the field at the end of a three-over stint.
Saim Ayub and Shan Masood, who both made 28, put on 49 for the first wicket before Rabada bowled Ayub.
Jansen followed up by having Masood caught at third slip and first innings top-scorer Kamran Ghulam caught at gully for eight before bad light stopped play.
Markram said it was a typical Centurion pitch, providing assistance for the fast bowlers.
"While I was batting it did feel that at any time the ball could nip past your edge," he said.
Markram cautioned South Africa would need to bowl well to press home their advantage on Saturday.
"If you're not going to land the ball in the right areas it’s still going to be nice to bat on," he said.
