Track and field events get underway Friday at Rio 2016, which arguably will be an uncomfortable moment for Russia’s Olympic team.
Russia was suspended from track and field events by the International Association of Athletics Federations in November 2015 amid allegations of state-sponsored doping.
One Russian athlete — Darya Klishina — will compete at Rio 2016, though the long jumper won’t be in action until Tuesday.
The 25-year-old is allowed to compete in the Olympics as she trains in the US and has undergone regular drug tests over the last two years.
Twenty four gold medals will be up for grabs across 19 sports Friday, with Michael Phelps, the most decorated Olympian of all time, looking for yet more gold as he takes to the pool again.
Here are four events to keep an eye out for on day.
Swimming
Phelps is expected to resume his rivalry with South African Chad le Clos in a battle for gold in the 100 meters butterfly.
The American beat Le Clos Tuesday to retake his 200m butterfly title, with the South African finishing fourth.
Katie Ledecky will also be back in action as she swims in the 800m freestyle, an event where she is the reigning Olympic champion and world record holder.
Ledecky is enjoying a fantastic second Olympic Games, having already won three gold medals and set a world record in the 400m freestyle.
Athletics
Team GB’s Jessica Ennis-Hill will be in action on day one of the heptathlon alongside teammate and rival Katarina Johnson-Thompson.
Defending Olympic champion Ennis-Hill will be looking to repeat her spectacular performance at the last Games as the heptathletes begin the day with the 100m hurdles. She famously set a British record in the same event at London 2012.
The 30-year-old won gold in 2015 at the World Championships in Beijing, just over a year after giving birth to her first child.
The first track and field medal up for grabs is in the women’s 10,000m with reigning champion Tirunesh Dibaba expected to battle it out with fellow Ethiopian Almaz Ayana for gold.
Cycling
One of the blue ribbon events of the track cycling competition at Rio 2016 will see reigning world champions Australia up against reigning Olympic champions Great Britain.
GB will be led by four time Olympic champion and former Tour de France champion Bradley Wiggins.
This is one of the most anticipated rivalries of the opening week of the games between two nations who have gone toe-to-toe in the velodrome for over a decade, winning 14 of the last 15 world championships in the team pursuit between them.
Judo
Judo is set to come to a close on Friday as the heavyweights take to the mat in the Carioca arena.
It has been a hugely eventful Olympic judo competition which included the first Olympic medal for Kosovo and some inspirational performances from two Congolese refugee judokas.
Eight time world champion and reigning Olympic champion Teddy Riner of France is expected to star on the men’s side.