Kgatlana netted two of her team's six goals including the last-gasp scorcher that dramatically dumped Italy out of the tournament.
"Well, it requires the same as always from me, we help each other at the back, we cover each other's back and I think (Sunday) it will be very important to have each other's back," said Van der Gragt.
The ninth-ranked Oranje topped Group E with two victories and a draw with two-time reigning champions United States.
Coach Andries Jonker said his squad had stopped "very fast attackers" versus Portugal at the World Cup, and in friendlies against Costa Rica and Poland - all Dutch victories.
"It's a matter of choosing positions, helping each other and having a keeper that pays attention," Jonker said.
"So far, we've had things under control. It's not that we're getting confused with this fast attacker from South Africa, but we have taken it into account and we're preparing for that."
The Dutch are ranked 45 spots above South Africa's Banyana Banyana, but this tournament has shown no team can be overlooked.
"It will be another fight at this world championship between a so-called smaller country - many people in women's football will consider South Africa smaller - and a bigger, not from the size but from history, and I think it will be another fight between two countries who have just one desire, fly to New Zealand (for the quarter-finals)," Jonker said.
Asked why the Netherlands are so consistent in tournaments, Van der Gragt said her side is built for the long haul.
"We spend a lot of time together," she said. "We only have each other because family is not there. There's good dynamics within the team . . . and we also will stick up for each other and that turns us into a solid tournament team.
"We're quite close and we're willing to fight for each other on the pitch."
The Dutch were back on the practice pitch on Saturday after Friday's long travel day from Dunedin to Sydney.
"I had this idea that this will be the world championship of football but also flying," Jonker said of his team's schedule. "But my attitude was straight away okay, just let this happen, go with the flow."
