US sprint king Noah Lyles launched his campaign for 100m glory Saturday, recovering from a slow start to come through his heat at the Paris Olympics, where a gender row in boxing rumbled on.
In other action, gymnastics legend Simone Biles vaults for a third gold on a packed day in Paris that will also see Sha'Carri Richardson sprint for redemption in the women's 100m.
The 27-year-old Lyles was one of the last out of the blocks in his heat but powered through the field, finishing second to Britain's Louie Hinchliffe in a time of 10.04sec.
Jamaica's Kishane Thompson looked in ominous form, running 10 flat but easing down significantly in the final stages.
Italy's Marcell Jacobs, who won a surprise gold in Tokyo, also laboured through his heat and just scraped through in a time of 10.05 sec.
In the women's race, flamboyant US track star Richardson is the reigning world champion over 100m and the fastest in the world this year with a brisk 10.71sec under her belt.
The 24-year-old Texan, aiming to become the first American since Gail Devers in 1996 to win Olympic 100m gold, sailed through her heat on Friday in 10.94sec.
Richardson is competing in Paris three years after her Olympic dreams in Tokyo were wrecked by a positive test for marijuana following her victory at the US trials.
The semi-finals and final of the women's 100m both take place on Saturday evening, with Saint Lucia's Julien Alfred looking like Richardson's main rival.
The second full day of athletics in Paris also includes the women's triple jump, the men's shot put and the conclusion of the men's decathlon.
Off the field of play, a simmering scrap over gender in boxing refused to go away, with IOC President Thomas Bach peppered with questions at a Saturday morning news conference.
The Algerian boxer at the centre of the row, Imane Khelif, fights at 1522 GMT, with a medal guaranteed if she wins.
Khelif's 46-second victory over Italy's Angela Carini sparked a row that spilled beyond the ring, with politicians and celebrities weighing into the controversy.
The International Boxing Association disqualified Khelif at last year's world championship, saying she had failed an unspecified gender eligibility test.
There is no suggestion Khelif identifies as anything other than a woman and Bach called for an end to the scrap, that has also impacted Taiwan's Lin Yu-ting.
"We are talking about women's boxing. We have two boxers who were born as women, who have been raised as women, who have a passport as a woman and who have competed for many years as women," said Bach.
Hungarian boxer Anna Luca Hamori, who faces Khelif next, wrote on Facebook: "In my humble opinion I don't think it's fair that this contestant can compete in the women's category."
But back home, both women won firm backing.
"She hasn't done anything wrong, that's the way she is -- it's unnecessary to attack her appearance," computer engineer Hannah Huang told AFP as he watched Lin at a Taipei sports bar.
In Algeria, Khelif's father Omar told AFP he had raised his daughter "to work and be brave."
"Since she was little her passion has always been sport," he said.
After her harrowing Olympic experience in Tokyo, where she withdrew from multiple events because of the mental block gymnasts call the "twisties", Biles already has two golds under her belt in the French capital.
The 27-year-old, who has won team gold and the all-around title in Paris, now tackles the vault final, which again pits her against defending champion Rebeca Andrade.
The US superstar knows she faces serious competition from the Brazilian.
"I don't want to compete with Rebeca no more. I'm tired!" Biles said after she secured the all-around title. "It's way too close."
In the pool, Katie Ledecky, now the most decorated US woman Olympian, seeks to add 800m freestyle gold to her 1500m title on the penultimate evening of swimming.
And on the clay courts of Roland Garros, Zheng Qinwen takes on Donna Vekic with a chance to win China's first tennis singles gold.
A total of 29 golds are up for grabs on Saturday, with France, Australia, Britain and the United States chasing current medal table leader China.
