A big upset in Rio.

Top seeded Serena Williams is done in the women's singles after falling in straight sets to Elina Svitolina of Ukraine.

Svitolina, ranked 20th in the world, got a break in each set, winning 6-4, 6-3.

Williams is now out of the Olympics altogether after the third round loss.  She and sister Venus were beaten in the first round of women's doubles.