Serena Williams upset in third round

Olympic champion and world number one Serena Williams tumbled out of the Rio de Janeiro singles competition in the third round today in a shock defeat to Ukraine's Elina Svitolina.

Svitolina, who is ranked 20th in the world, stunned the London Games gold medallist 6-4 6-3 to record a memorable victory against the American, who has won 22 grand slam singles titles.

"It's an unreal feeling for me. This is just a perfect moment," said Svitolina, who will face Czech Republic's Petra Kvitova in the quarterfinals.

Williams was visibly frustrated throughout the match as she struggling to find her range, making 37 unforced errors compared to 17 by Svitolina.

Late in the second set, Williams served five double faults in a single game, which drew gasps from a shocked audience.

Williams, who has won three women's doubles Olympic titles with sister Venus, was also eliminated with her sister from the doubles on Sunday.