OMNISPORT 

Serena Williams overcame a shaky start to her Olympic defence to ultimately dominate Australia's Daria Gavrilova in Rio de Janeiro.

The top seed - and four-time Olympic gold medallist - had to scrap to hold serve in the opening game, and then coughed up an immediate break of serve, but quickly settled into a rhythm to beat the world number 46 6-4 6-2.

Williams' older sister Venus was stunned in the first round by Kirsten Flipkens on Saturday and the three-time defending doubles champions will begin the defence of their crown later on Sunday against Czech pair Lucie Safarova and Barbora Strycova.

Gavrilova found early joy by coming to the net and intercepting Williams' power strokes, but she was pushed further and further back as the world number one took control.

Williams remained shaky on serve, broken to love when 5-3 up in the opener, but her 22-year-old opponent could not make it count and Serena swiftly broke back to take a 1-0 lead.

The second set was one-way traffic, Gavrilova frantically flying across the baseline as Williams boomed shots around the court - the Australian tumbling on several occasions as her efforts became more frantic.

And her fatigue showed through as Williams wrapped up the final set on the back of five points, each earned by wayward Gavrilova shots.