When Inglis scored just after the interval the match was over as a contest. In front of 11,570 fans, the Knights were a shadow of the side which produced one of the upsets of the season over premiers the Sydney Roosters last Friday night.
Missing Jarrod Mullen, James McManus, Akuila Uate and Darius Boyd, the Knights brought some respectability to the scoreline with efforts to Jake Mamo in the 50th minute in the steamy conditions at Barlow Park, and Adam Clydsdale two minutes later.
It was all Souths again after that, as Johnston scored three tries in 16 minutes before Auva'a crossed for his second as the Rabbitohs notched their half century.
The Rabbitohs' Kiwi rake Issac Luke also starred for South Sydney in a man-of-the-match effort.
The victory puts the Rabbitohs behind premiership frontrunners Manly, and equal with Penrith but ahead on for-and-against.
Souths face the Sea Eagles in a top-of-the-table clash at the Sydney Cricket Ground on Friday night.
The loss leaves the Knights two points ahead of last-placed Cronulla.
Souths 50
Knights10
- AAP