Hermoso's first penalty kick tied it in the 69th minute after South Africa captain Janine Van Wyk was called for a hand ball.
One other penalty became as soon as awarded to Spain following a VAR evaluation, which seen Nothando Vilakazi booked for the 2nd time and sent off for the first red card of the match.
Thembi Kgatlana put South Africa ahead on 25 minutes with a curling strike from the edge of the box, but Atletico Madrid forward Hermoso twice scored from the spot as Spain fought back.
It was the second Group B match of the day.
Earlier on Saturday afternoon, two-time winners Germany claimed a hard-fought 1-0 win over China in their first Group B match in Rennes, as teenage midfielder Giulia Gwinn scored the only goal on the 66th minutes.
The sides both struck the woodwork before the deadlock was broken, Yang Li hitting the upright when presented with a fine opportunity to score after opponent Carolin Simon had rattled the bar in a tense clash. China failed to take advantage of pressure they created in the second half.
In the final game of the evening, Norway beat Nigeria 3-0 with two goals and an own goal in the first half, trailing top-rated hosts France in Group A on goal differences.
South Africa is bottom of Group B and next face China in Paris on Thursday.
The 1995 winners played without Ada Hegerberg, the 2018 Fifa Ballon d'Or victor who stepped down from the national team because of what she says are differences in the way the Norwegian federation treats the men's and women's teams.
Nigerian defender Faith Michael was stretchered off after a collision with team-mate Tochukwu Oluehi.
New Zealand start their tournament with a match against the Netherlands on Wednesday at 1am.
128GB Google Pixel 3 XL for just $649.99, that's $350 off
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Former Red Sox star David Ortiz shot in Dominican
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After netting four times in six minutes shortly after the restart, they then added six more goals in the last 16 minutes. Afterward, former US goalkeeper Hole Solo called Sweden "cowards" for bunkering on defence.
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