Bolt eyes history after Phelps heroics

Usain Bolt is chasing a place in Olympic history on Sunday as the battle to be crowned world's fastest man takes centre stage following Michael Phelps' record-breaking exploits in the swimming pool.

Twenty-four hours after American swimmer Phelps brought the curtain down on his extraordinary career with a record 23rd gold medal, Bolt will attempt to complete the first leg of an unprecedented "triple-triple" in the 100m at the Olympic Stadium.

With semi-finals scheduled at 9pm local time (0000 GMT), Bolt is poised to line up for the final at around 10:25pm where he will aim to clinch a third consecutive 100m crown after wins in 2008 and 2012.

The Jamaican superstar made his opening bow in Rio during Saturday's heats, coasting to victory in 10.07sec.

His biggest challenger is expected to be Justin Gatlin of the United States, the 2004 Olympic champion who has served two suspensions for doping offences during his career.

The 100m final is one of four track and field gold medals on offer on Sunday, with the men's 400m and women's triple jump also up for grabs.

Kenya's Jemima Sumgong won the first athletics gold of the day, making light of searing heat to triumph in the women's marathon, which finished at Rio's Sambodromo, the home of the city's annual carnival parade.

Sumgong came home in a time of 2hr 24min 04sec to clinch Kenya's first-ever women's marathon gold.

"It was very hot but everybody had to get through the heat. I had to control my body and listen to my body very carefully," said Sumgong.

- Lochte, US swimmers robbed -

Bahrain claimed only their second medal in any sport when Kenyan-born Eunice Kirwa took silver, 9sec adrift of Sumgong, while defending world champion Mare Dibaba of Ethiopia won bronze.

The race notably saw the participation of Estonian triplets Leila, Liina and Lily Luik, who finished way down the field as they struggled to adapt to conditions.

"It was so hard. I saw everybody stopping and everybody suffered," said Lily, the first of the triplets home in 97th place in 2hr 48min 29sec.

The marathon was subject to a security alert just before the finish when a group of protesters scaled barriers and ran onto the course before being intercepted by police on motorbikes. Runners were not affected by the protests.

In a separate incident, police carried out a controlled explosion on a "suspect package" found near the marathon course.

Security throughout the Rio Games has proved a major headache for organisers, with several competing teams complaining of thefts and street crime in the recession-hit metropolis.

The latest to fall victim to Rio's soaring crime rate was US swimmer Ryan Lochte and three team-mates, who were robbed at gunpoint by criminals who pulled over their taxi posing as police.

"They pulled out their guns, they told the other swimmers to get down on the ground -- they got down on the ground. I refused, I was like we didn't do anything wrong, so -- I'm not getting down on the ground," Lochte told NBC News.

"And then the guy pulled out his gun, he cocked it, put it to my forehead and he said, 'Get down,' and I put my hands up, I was like, 'Whatever.' He took our money, he took my wallet -- he left my cell phone, he left my credentials."

Elsewhere Sunday, Martina Hingis's dream of a golden Olympic return after a 20-year absence came to an end in the tennis women's doubles final.

Former Swiss world number one Hingis, 35, who last played in the Olympics in 1996, lost with partner Timea Bacsinszky in the final of the women's doubles to Russian duo Ekaterina Makarova and Elena Vesnina.

In gymnastics, Britain's Max Whitlock won a gold medal in the floor exercise, scoring 15.633 points. Brazilian duo Diego Hypolito (15.533) and Arthur Mariano (15.433) won silver and bronze.