Double Olympic taekwondo champion Steven Lopez of the United States eased through his first round bout on Friday, chasing a gold medal to complete a family treble after siblings Mark and Diana won a silver and a bronze.

Lopez despatched Turkey's Bahri Tanrikulu in a rematch of their Athens championship bout, landing two scoring kicks to win 3-0 and book a quarter-final place against European bronze medallist Mauro Sarmiento of Italy.

"I think it should have been the final," Lopez said after the 80-kg match.

The rangy 29-year-old American is favoured to win a record third Olympic gold and become the third Lopez to win a taekwondo medal at these Games, after younger brother Mark and sister Diana took silver and bronze on Thursday.

The first-round win was also vengeance for Diana's defeat at the hands of Tanrikulu's younger sister Azize, who took silver in the women's 58-kg division.

"My sister did well and I am proud of her. But in the back of my mind, I (had) to avenge my sister's loss," Lopez said.

The Lopez family are bidding to become the first set of three American siblings to win medals in the same sport at the same Games. Mark Lopez won silver in the men's 68-kg class.

In the women's 68-kg category, Athens bronze medallist Hwang Kyung-seon of South Korea cruised to a quarter-final place with a 5-1 victory over the United Arab Emirates princess Sheikha Maitha Almaktoum.

The hot favourite and two-time world champion will take on European champion Sandra Saric of Croatia for a place in the semi-finals.