Lee departed on the ball of Suleeporn Laomi after scoring 101 runs off 60 balls. Her innings was laced with 16 fours and 3 sixes. Luus, meanwhile, scored 61 not out off 41. Her knock was helped by 5 fours and 2 sixes.
Earlier, South Africa skipper Dane van Niekerk on Friday won the toss and opted to bat first.
"We want to get a good score on this surface. We thought getting runs on the board and defending would be the best thing against their bowling," said South Africa skipper after winning the toss.
Knight's 108* is the third-highest individual score in the overall history of the Women's T20 World Cup.
Both the teams are unchanged and are playing with the same XIs that featured in their respective previous matches.
