Monica Puig beat Petra Kvitova to seal a place in the final of the women's tennis, where she will compete for Puerto Rico's first Olympic gold.
The competition in Rio was blown wide open by favourite and reigning champion Serena Williams' early exit and Puig may transpire to be the main beneficiary after beating her Czech opponent 6-4 1-6 6-3.
Puig, ranked 34th in the world, has just one WTA title to her name and has never progressed past the fourth round at a grand slam.
Her prospects did not look good initially at the Olympic Tennis Centre as Kvitova stormed into a 3-0 lead in the opening set, but Puig dug deep and showed greater resolve on the key points to seize the advantage.
The Puerto Rican also endured a poor start in the second set and could not muster another comeback.
Puig made the initial break in the third set, but immediately surrendered the initiative, repeating the pattern in games six and seven.
Still, it did not deter the 22-year-old, who made the scoreboard pressure tell as she won a mammoth rally en route to yet another break before serving out the match.
She will face the winner of the other semi-final between Angelique Kerber and American Madison Keys.