The 34-year-old Mothibi spoilt defending champion Bongmusa Mthembu’s attempt at a fourth consecutive title.
She became the first female to break through the six-hour barrier in the ‘up’ run.
Nadal admits the prospect of winning a 12th Roland Garros title and 18th major on Sunday would have once just seemed liked an "incredible" dream.
"This is fantastic for the sport," said Hamilton. "I love to fight with another team and today was just so close.
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