Serena Williams has been dumped out of the women's singles at the Olympic Games after losing in straight sets to Elina Svitolina.

The world number one had been hoping to add to the gold medal that she won in London in 2012 but her serve let her down as she was outplayed by the 15th seed, who had needed three sets to defeat Great Britain's Heather Watson in the previous round.

Williams won just four points behind her second serve as Svitolina broke twice for a one-set advantage and she looked on course for a routine win when moving a break ahead during the early stages of the second set.

The American hit back to level at 3-3 but double faults were being conceded with regularity and Svitolina was able to strike twice more to register a famous 6-4 6-3 win.

Svitolina will now play Petra Kvitova for a place in the semi-finals.