"People laugh at me but I genuinely don't read the papers."
Khawaja eventually fell for 145 early on day three of the day-night test.
He reached three figures on day two, resisting the Proteas' star-studded pace attack to build a first-innings lead of 124 runs for Australia.
The impressive knock started late on day one, when Khawaja was forced to open after a timely declaration from Faf du Plessis.
David Warner was off the field receiving treatment late in South Africa's innings.
"The boys are calling me nightwatchman at the moment, having a few jokes about it," Khawaja said as he prepared to bat for a third straight day.
"It happened all so quickly. When I saw Faf and Faf heard what was going on, I was like crap I'm going to be opening ... Faf declared the next ball."
Khawaja put a high price on his wicket, leaving the ball frequently as Australia crawled to 2-46 after 26 overs.
"I was about 12 off 70 balls and looking up at the scoreboard that's never nice. But I stayed out there long enough to score some runs which was pleasing," he said.
- AAP