Fifth golden gong for Felix?

Allyson Felix had wanted to pull off Michael Johnson's double - gold medals in both the 200m and 400m - but she failed to qualify for her preferred 200m after struggling with an ankle injury.  A win for Felix would be her fifth Olympic gold medal, the most ever for a female track athlete.

Rudisha show back in town

David Rudisha was imperious four years ago when he won 800m Olympic Gold at London 2012 in a world-record time of 1:40.91. The 27-year-old Kenyan arrived in London unbeaten that year over the distance and promptly blew everybody away. This year has been a little more erratic, but his world-leading time of 1:43.35 will stand him in good stead to become the first man since Peter Snell in 1964 to retain an Olympic title over two laps.
In a league of his own, will anyone even make it into David Rudisha's photo frame? (Photo: Getty Images/Buda Mendes)

Olympic debut for Britain's Ali

Walking into the ring with a name like Muhammad Ali may well add unnecessary pressure to an already tense situation but this 20-year-old from Bury in the north of England comes to Rio 2016 brimming with confidence. Hailing from the same boxing club as Amir Khan, who won lightweight silver for Great Britain at Athens 2004, Ali is another fighter with quick hands gunning for gold.

It's hammer time

In one smooth throw Poland's Anita Wlodarczyk’s easily achieved the qualifying distance and threw her hammer three metres further than her closest rival. Wlodarczyk throws using the glove of close friend Kamila Skolimowska, who died in 2009 after winning gold at Sydney 2000 as a 17-year-old. The bookmakers have her as favourite to win gold, so the big question is: can she win and better her own world record? 

Polish world record holder Anita Wlodarczyk looked impressive in qualifying (Photo: Getty Images/Dean Mouhtaropoulos)

Carioca boost for Zanetti? 

São Paulo native Arthur Zanetti should find a sympathetic audience when he performs at the Rio Olympic Arena today. The crowd watching artistic gymnastics have been a major factor in Brazil's success at these Games thus far. Even non-Brazilian athletes have drawn energy from the boisterous congregation. Recalling performing in front of his home crowd last year, Zanetti told Rio 2016: "Their energy helps a lot. It gives me extra strength that I didn’t have before." 

Arthur Zanetti is hoping for a repeat of his gold medal performance at London 2012 (Photo: Getty Images/Matthew Stockman)

Omnium optimum for thrills and spills

This event is considered to be the 'decathlon of cycling'. Designed to determine the best all-round cyclist, the omnium consists of six different disciplines and has become a firm crowd favourite since its inclusion at London 2012. Great Britain's reigning Olympic champion Laura Trott will feature, as well as sprint king Mark Cavendish, who is seeking his first Olympic medal. He has a lot prove. In 2008 he was the only member of the GB cycling team to leave Beijing empty handed and four years ago failed to win a medal in the time trial.

Biles on the beam 

It’s hard to believe Simone Biles is currently competing at her first Olympic Games as she attempts to win her fourth gold of Rio 2016. The 19-year-old has dominated the gymnastics world for the past couple of years, and she looks set to assert that dominance on the balance beam. She retook the lead for her team in the all-round event with a stunning performance on the beam. Her chief rival is team-mate Laura Hernandez.

Olympic giants: USA team-mates Simone Biles and Michael Phelps (Twitter)

Copacabana swimming

While the Serpentine in Hyde Park did provide its own unique charm at London 2012, there are not many backdrops that can match Rio de Janeiro when it comes to the 10k open water swim. The women taking part in this marathon set off and finish at Copacabana Fort. The area is known for choppy surf and strong currents, which should make for an interesting race and an unpredictable winner. Favourite to win is Italy's Simone Ruffini.

Forte de Copacabana where the open water begins and ends (Wikimedia)