South Africa were 145 for three at tea in Port Elizabeth after losing captain Graeme Smith and Hashim Amla inside the first six overs.
Elgar (61 not out) and Du Plessis (55) put on 112 for the third wicket - only the second century stand against Australia since the start of their 5-0 Ashes sweep against England earlier in the summer.
The left-handed Elgar, opening the batting in place of the ill Alviro Petersen, saw Smith and Amla depart before he opened his score off the 20th ball he faced.
Elgar had faced 146 balls by tea, hitting six fours and two sixes, with both sixes against off-spinner Nathan Lyon
Ryan Harris made the first breakthrough when Smith played across the line and was leg before wicket for nine.
Johnson followed up with his 50th Test wicket in seven matches since the start of the Ashes series against England when Amla was beaten for pace and trapped leg before with a full-pitched delivery.
They picked up the pace after lunch, adding 59 in an hour before Du Plessis was out off the first ball of the afternoon drinks break, turning a ball from off-spinner Nathan Lyon straight into the hands of Steve Smith at short leg.
You’ve reached your limit of {{free_limit}} free articles this month.
Subscribe now for unlimited access.
Already subscribed? Log in
Subscribe to read the full story →
Smart Quarterly
₹900
3 Months
₹300/Month
Smart Essential
₹2,700
1 Year
₹225/Month
Super Saver
₹3,900
2 Years
₹162/Month
Renews automatically, cancel anytime
Here’s what’s included in our digital subscription plans
Exclusive premium stories online
Over 30 premium stories daily, handpicked by our editors


Complimentary Access to The New York Times
News, Games, Cooking, Audio, Wirecutter & The Athletic
Business Standard Epaper
Digital replica of our daily newspaper — with options to read, save, and share


Curated Newsletters
Insights on markets, finance, politics, tech, and more delivered to your inbox
Market Analysis & Investment Insights
In-depth market analysis & insights with access to The Smart Investor


Archives
Repository of articles and publications dating back to 1997
Ad-free Reading
Uninterrupted reading experience with no advertisements


Seamless Access Across All Devices
Access Business Standard across devices — mobile, tablet, or PC, via web or app
