The match was the first in a triple-header at the spiritual home of New Zealand rugby on Saturday, where a record crowd for a standalone women's sporting event in the country is expected before the day is out.
Only a smattering of fans gathered in the 50,000-seat arena at the start of the first Pool C clash, but they were treated to some fine early tries as France, who finished third at the last two World Cups, took a 19-0 lead after 17 minutes.
Sansus ran through a gaping hole in the defence off the back of a rolling maul, centre Emilie Boulard latched onto a chip ahead from flyhalf Caroline Drouin and winger Gabrielle Vernier ran in an intercept for the third score.
South Africa, playing in their first World Cup since 2014, had some good moments in the scrum and at the maul, but it was not until 10 minutes after half time that they got on scoreboard when winger Nomawethu Mabenge finished well in the corner.
That charged the 11th ranked South Africans with confidence and they repelled attack after attack from the French until a quickly-taken penalty allowed Sansus to breach their line for a second time in the 68th minute.
Four minutes later and the French were in again after number eight Romane Menager made a break up the middle of the park and found Drouin inside her with an offload, allowing the playmaker to race away and cap her fine performance with a try.
Drouin was not finished yet and her crosskick gave debutante winger Joanna Grisez the simplest of finishes for the sixth try in the last few seconds.
Top-ranked England take on World Cup debutantes Fiji in the second match in Pool C later on Saturday before hosts and defending champions New Zealand face neighbours Australia in the final clash of the day.Â
