RIO DE JANEIRO, BRAZIL - AUGUST 09: Serena Williams of the United States reacts during a Women's Singles Third Round match against Elina Svitolina of Ukraine on Day 4 of the Rio 2016 Olympic Games at the Olympic Tennis Centre on August 9, 2016 in Rio de Janeiro, Brazil. (Photo by Clive Brunskill/Getty Images)

Defending Gold medal champion Serena Williams has been bundled out of the Rio Olympics by Ukrainian Elina Svitolina.

Williams lost her third round match 6-4, 6-3, after earlier in the week losing the first round in the doubles with sister Venus.

Meanwhile, Australian Sam Stosur is also out after a straight sets loss to Australian Open champion Angelique Kerber.

The world No.2 advanced to the fourth round with a 6-0, 7-5 win over the Aussie to end her medal hopes in the singles compeition a clinical performance.

Kerber will face Great Britain's Johanna Konta in the quarterfinals.

However, she is still a chance to win a medal for her country in doubles, with Stosur and John Peers set to take on Indian pair Sania Mirza and Rohan Bopanna in the first round of the mixed doubles.