South Korea edged Northern Ireland 1-0 in this morning's other Group C match to move to the top of the group. It means New Zealand must beat South Korea to earn a playoff for seventh, the highest possible finish for the Football Ferns in a lopsided three-pool format.
The top sides are all in the other two pools, leaving New Zealand to battle it out for the minor placings even though they finished second overall as recently as two years ago.
Readings made three changes to the side that beat Northern Ireland 2-0 in the first match, with Ria Percival, Hayley Moorwood and Betsy Hassett all handed starts in place of Anna Green, Kirsty Yallop and Annalie Longo.
Green, Yallop and Longo were used as second-half substitutes along with goalkeeper Rebecca Rolls who collected her 12th cap - 16 years after her 11th - and shared in a second-straight Ferns clean sheet with Jenny Bindon.
Katie Hoyle and Amber Hearn had the best chances to score but both missed the target and Yallop was denied by the South African keeper one-on-one in the last play of the game.
Readings said the most valuable lesson heading into an Olympic Games campaign was the need to remain adaptable while still backing their own style of play.
"At the Olympics we'll come up against at least three different teams all with different styles of football and we're going to have to adapt from one game to the next.
"We've already played a British team here, an African team and now we're up against an Asian team with a completely different style of football.
"What we need to do is make sure we adapt from game to game, and within games and we are getting invaluable exposure to that at tournaments like this one.
"We are a team who likes to play and who is looking better and better when doing that but there are times when we can mix it up a little bit."
South Africa have already qualified for London - notably ahead of traditional African powerhouses Nigeria and Ghana - while New Zealand face a home and away playoff on March 31 and April 4 against the winner of this week's Oceania qualifying tournament in Tonga.
Papua New Guinea and the hosts claimed opening wins yesterday to emerge as New Zealand's most likely playoff opposition.
"If we qualify for the Olympics, we've got as much chance of drawing South Africa as any other team," Readings said.
"They are a team with a lot of backing behind it, and they knocked out some very good teams to qualify so all in all it's a solid result this far out from London."