PARIS, France — A thrilling open-water swim in the River Seine kicked off Friday's Olympic action in Paris, which will later see Algerian gender eligibility row boxer Imane Khelif go for gold.

With just three days left of the Olympics, a packed athletics schedule features sprint relays, as the US seeks to maintain dominance in the 4x100m relay — even without Covid-hit 100m champion Noah Lyles.

In the day's first event, 31 men plunged into the waters of the Seine for the 10k marathon swim, as officials again deemed the river clean enough to compete.

A hard-fought race finished with a sprint between Hungary's Kristof Rasovszky and Oliver Klemet of Germany, just won by the Hungarian, nicknamed the "Balaton Shark" after his club.

David Betlehem, also from Hungary, won bronze, pipping Italy's Domenico Acerenza by a fingertip after a grueling battle against the strong currents in the Seine.

The water quality in the Seine has been a major talking point during the Games, with training sessions canceled and the men's triathlon postponed after elevated pollution levels.

'Etched in the annals'

On the track, a nail-biting women's heptathlon builds to a crescendo, with Britain's Katarina Johnson-Thompson holding a tiny 48-point lead over reigning Olympic champion Nafissatou Thiam of Belgium.

The evening session will see 4x100m relays for the men and women, with the all-conquering US hot favorites in both, even after sprint king Lyles withdrew after contracting Covid.

"It is not the Olympic(s) I dreamed of but it has left me with so much joy in my heart," said the brash American.

Lyles came third in the 200m final on Thursday, with Botswana's Letsile Tebogo claiming gold for Africa's first-ever 200m crown.

President Mokgweetsi Masisi gave the whole country the afternoon off to celebrate the gold which he said would be "etched in the annals of the history of the Republic."

In Friday's women's 10,000m final, Dutch runner Sifan Hassan will attempt to defend her crown after coming up short in her bid for a historic long-distance treble.

Hassan could secure only bronze in the 5,000m final on Monday and also competes in the marathon on Sunday.

In the final event of the night, world record-holder Karsten Warholm from Norway is clear favorite to defend his title in the men's 400m hurdles.

'Achieve my dream'

The boxing ring will be the center of attention late on Friday when Khelif, 25, takes on China's Yang Liu in the 66kg final.

A row over the eligibility of Khelif and Taiwan's Lin Yu-ting has overshadowed the Olympic boxing tournament and the Games as a whole.

The International Boxing Association disqualified both from last year's world championships after they failed gender eligibility tests but both were cleared to fight in Paris.

Both boxers have fought on the women's circuit for years and competed at the Tokyo Games without controversy.

A row erupted when Khelif stopped her Italian opponent after just 46 seconds, with celebrities and politicians weighing in to make baseless claims over her gender.

But Khelif has won the support of fans in Paris, with cries of "Imane, Imane" ringing out repeatedly before and during her semi-final bout on Tuesday.

"I am like all athletes, I am here to achieve my dream," she said.

Lin fights on Saturday in a different weight category.

'Goosebumps'

Other crunch events see Thierry Henry's France take on Spain in the men's football final at the Parc des Princes, aiming for the first gold since 1984.

They have conceded just a single goal in five matches and Henry admits he does not want his Olympic dream to end.

"I think it's going to be difficult waking up," he said. "Every night I watch and get goosebumps when I see the guys win."

In diving, China are targeting gold in the women's 3m springboard as they close in on clean sweep in Paris, with victories in all six events so far.

Defending champions the Netherlands take on China in the women's hockey final, chasing their fourth title in five Games after the Dutch men's team won gold.

History will also be made when the first Olympics medals are won in the breaking competition.