Chen’s failed test after narrowly missing a bronze medal in the women’s 100 meter butterfly was announced as athletics headed into the Olympic spotlight needing an antidote to its own doping scandals.
Phelps was magnificent again in retaining his 200m individual medley title, leaving old rival Ryan Lochte stranded in fifth place. Even second place Kosuke Hagino was nearly two seconds back.
Afterwards, the 31-year-old wagged four fingers to show his four gold medals so far in Rio. That has taken him to an incredible 22 Olympic titles and 26 medals overall.
“I say this a lot, but every single day I’m living a dream come true. As a kid I wanted to do something that no one had ever done before and I’m enjoying it,” said Phelps.
Simone Manuel of the United States and Penny Oleksiak of Canada shared a dead heat victory in the women’s 100m freestyle. Manuel is the first African-American woman to win an individual Olympic swimming gold.
But the spotlight quickly turned to 18-year-old Chen, who won a world championship gold medal last year in the 4×100 medley team.
The Chinese Swimming Association said Chen tested positive for the diuretic hydrochlorothiazide after Sunday’s 100m butterfly final, China’s official Xinhua news agency reported.
Chen came fourth just 0.09 second behind bronze medalist Dana Vollmer of the United States.
Diuretics can be used to mask other banned substances.
The CSA said Chen, who was due to take part in 50m freestyle heats on Friday, had asked for a second test on the sample to be carried out and a hearing in the case.
The CSA said it has “demanded full cooperation from Chen in the investigation.”
“The CSA resolutely opposes use of banned substances,” it added.
But alongside the storm that has engulfed Russia over accusations of “state-sponsored” in two World Anti-Doping Agency investigations, China has also been accused by some rivals.
Australia’s Mack Horton called Sun Yang, China’s most successful swimmer, a “drugs cheat” this week, setting off a social media firestorm in China.
The United States strengthened its lead in the Olympic medals table finishing Thursday with 16 golds, five ahead of China.
Simone Biles added the women’s all around gymnastics title to victory in the team event.
The 19-year-old is chasing five gold medals in Rio, and few would bet against the 1.45m (4ft 9in) Texan adding to her tally in the apparatus finals to come.
Golf started its return performance at the Rio Games.
Australian Marcus Fraser was the early pace-setter with a 63 in the first Olympics round since the 1904 Games in St. Louis. England’s Justin Rose marked the occasion with a hole-in-one.
Rugby also made its return and Fiji’s sevens team hammered Britain 43-7. The South Pacific nation’s first ever gold medal sparked wild celebrations at home.
The specter of doping also loomed over the athletics competition, which starts Friday. The International Olympic Committee confirmed that a second Kenyan coach had been sent home from the Games for a doping offence.
Media reports named the offical as sprint coach John Anzrah, saying he had attempted to impersonate an athlete during a doping test.
Athletics starts at the Rio Olympics on a mission to win back fans after the Russia and Kenya doping scandals of the past year.
With Usain Bolt looming as the biggest draw of the Olympics, three athletics golds will be won on the first day at the Olympic stadium.
Ethiopia’s 10,000 star Tirunesh Dibaba, 31, will become the first woman to win three consecutive golds in an individual athletics event if she retains the crown won in London four years ago.
New Zealand’s Valerie Adams could also become the first woman to three titles if she can get the shot put title before Dibaba. The women’s 20km race walk will also be decided while Jamaica’s Shelly-Ann Fraser-Pryce starts the heats as she bids for a hat-trick of 100m sprint victories.