After more than 1,600 days away from competition, China's disgraced Olympic champion swimmer Sun Yang has returned to winning ways, eyeing redemption following a controversial anti-doping rule violation.

With a long, career-threatening suspension now behind him, the three-time Olympic champion freestyler, proved over the weekend that, even at the age of 32 and without systematic training for over four years, he remains an elite competitor at the national level and his story is far from finished.

He won his first official race in 55 months on Sunday, clocking 3 min and 49.58 sec to finish first in the men's 400m freestyle final at the national summer championships, a second-tier domestic meet in Hefei, East China's Anhui province — an event that would never normally find itself under such scrutiny, were it not for Sun's return.

The most decorated, and perhaps the most controversial, men's swimmer in China, has refused to be written off in the pool after serving a four-year-and-three-month ban imposed by the Court of Arbitration for Sport, which began in February 2020, for a doping-control rule violation that occurred in September 2018.

His winning mark on Sunday was nowhere near his 400m best of 3:40.14, which secured China's first men's swimming Olympic gold medal at London 2012 and still stands as the Olympic record, yet it was enough of a testament to his unremitting and resilient effort over the past four years.

Having maintained his innocence over the 2018 incident at multiple hearings and trials, Sun is relishing a second chance after pulling through a "tough rebirth".

"I got quite emotional. To be able to stand on top of a podium at my first meet in over four years, I feel like everything has paid off," said Sun, who was originally banned for eight years, before having the suspension reduced in June 2021 at a CAS retrial following his appeal.

"I owe a lot to my parents and my family, who have supported me all the way through all of the ups and downs," said Sun, who burst into tears after hugging his wife Zhang Doudou, a former rhythmic gymnast who married Sun last year, following Sunday's victory.

"I am not done yet for sure. I feel like I could've done better.

"This meet was just a test of my solo training without any competition. It was really a good start for my comeback.

"The past four years were so hard, tougher than being born again, which made me enjoy each and every race even more," said Sun, who only signed up to a single event at the championships.

The confirmation of Sun's appearance at the meet five days before his first heat resulted in a spike in ticket sales, with the price of scalped tickets for the Sunday evening session rising to four times their face value, according to local media reports. Fans were thrilled to see Sun's return, with the hashtag "Sun Yang wins 400m freestyle" quickly becoming one of the most trending topics on Chinese social media on Sunday night.

The last time Sun competed in an official competition was on Jan 19,2020, when he won the 400m final in 3:44.98 at a World Aquatics Champions Swim Series event in Beijing.

As an exceptionally efficient freestyler in his prime, Sun shot to fame by winning two golds in 400m and 1,500m on his Olympic debut at London 2012. He cemented his dominance in the discipline by adding a 200m gold at Rio 2016, becoming the first swimmer in history to collect Olympic titles in all the three distances.

He's also bagged 11 individual world championships titles since 2011, reigning supreme in freestyle swimming until the 2018 incident called an abrupt halt to his career.

A random out-of-competition drug test at Sun's residence in Hangzhou, Zhejiang province, in September of that year escalated into a fierce dispute between Sun and testers from IDTM, an agency hired by swimming world governing body World Aquatics, over the testers' authorization and eligibility, according to Sun.

Sun claimed he refused to cooperate only after finding testers were operating without adequate proof of ID, and were taking photos of him without his permission during what was supposed to be a confidential procedure.

In January 2019, World Aquatics ruled that Sun's refusal was reasonable, based on results of an independent panel's investigation, which found that the IDTM testers failed to show adequate proof of identification and authorization.

Two months later, the World Anti-Doping Agency appealed the initial ruling to CAS, where a panel of three judges determined Sun was guilty, imposing the eight-year ban in February 2020.

The Swiss supreme court set aside the ban in December of that year, following a successful appeal by Sun's attorney, who challenged the neutrality of Franco Frattini, chairman of the original CAS panel, who was deemed to have displayed an anti-China bias in comments posted by the Italian on social media.

The second hearing, in June 2020, saw the original ban reduced to four years and three months, yet still found that Sun had violated doping-control rules.

Sun was allowed to train during his suspension, but he was barred from doing so at a government-funded training facility, with a professional team, or any other Chinese state-sponsored athletes.

Having missed the past two Olympics in Tokyo and Paris due to the ban, Sun said he won't rule out any chance to represent China again at the 2028 Los Angeles Games.

"If there's an opportunity, I will go all out for it without any question. But, if I don't make it, I will accept what happens with a peaceful mind," said Sun, who has promised to try and qualify for next year's Chinese National Games first.

However, Sun's hopes of suiting up for Team China again seem almost impossible, at least for now, as any athlete banned for more than a year due to a doping violation is not eligible for selection for the national team, according to a national anti-doping management regulation enforced in 2021.