In 72 minutes, 19-year-old Polish Iga Swiatek made it 6-2, 6-1 against Argentine Nadia Podoroska.
Now Sofia Kenin or Petra Kvitova are waiting in the final.
Swiatek is the first Polish to reach the final in a grand slam in eight years.
The last time this happened was Agnieszka Radwanska at Wimbledon in 2012.
The 19-year-old, who is ranked 53rd in the world, has not yet lost a set in the tournament.