Sun Yang is optimistic 2020 will bring more Olympic glory as he waits for the cloud of his pending court case to lift.

On Tuesday, the 27-year-old opened the Olympic year with a narrow defeat in the Shenzhen leg of the new FINA Champions Swim Series, losing out to Lithuania's Danas Rapsys by three-hundredths of a second in the 200m freestyle.

Sun, the reigning Olympic and world champion in the event, seemed to have the gold around his neck with 50 meters to go, only for the late-surging Rapsys to overtake him and win in 1:46.50.

The result saw Rapsys avenge his final loss to Sun at last year's world championships, where the Lithuanian touched first but was later disqualified for a false start.

Sun, though, declared himself pleased with his performance, given he is in the middle of a tough winter training regime and is endeavoring to keep thoughts of the looming decision in his Court of Arbitration for Sport (CAS) case out of his mind.

"Today's result was actually not bad and it should be put into perspective that I am far from my best racing shape at the moment. I just approached the race as a practice," Sun told CCTV.

"I am OK with the time and I think I've done better on certain details, such as starting and turning, which I've been working on during the winter program.

"Hopefully, the hard work will pay off in March at the Olympic trials."

Sun's appearance in the new FINA series drew huge domestic media attention this week as the three-time Olympic champion had reportedly been set to skip the meet, with a CAS ruling on his doping case imminent.

At a November CAS hearing in Switzerland, Sun was accused by the World Anti-Doping Agency of failing to cooperate with doping testers at his home in September 2018. If found guilty, he faces a ban of two to eight years.

However, the 27-year-old remains optimistic that he will be cleared of any wrongdoing, with his sights firmly set on continuing his gold-winning streak at his fourth Olympics in Tokyo.

"The start of the Olympic year means something special for every athlete and I will take every possible opportunity, such as the Shenzhen meet, to gauge my training and try to improve upon each race," said Sun, who claimed the 400m and 1,500m free gold medals at the 2012 London Olympics and 200m free title at the 2016 Rio Games.

If free to compete in Tokyo, Sun will bid to add at least one more title, in either 200 or 400 free, to become the first Chinese man in history to win gold medals at three consecutive Olympic Games.

Sun said the best way of keeping his mind off the CAS ruling is to simply push harder in training every day and focus on his Tokyo preparations.

"My career goal now is to finish on top of the podium at three Olympics in a row," Sun told news portal people.cn last week after attending a pep rally for the Tokyo Games at the Chinese Olympic Committee's headquarters in Beijing.

"That will be an extremely tough challenge but I am going to enjoy the process. If I do the process right, I believe the result will take care of itself."

Citing their lack of authorization and credentials, Sun refused to cooperate with testers during an out-of-competition drug test conducted by FINA-contracted International Doping Test and Management on Sept 4, 2018 in Hangzhou, Zhejiang province.

Sun denied any physical confrontation with the testers and maintained his innocence at the CAS hearing, a procedure triggered by WADA's appeal against an earlier FINA ruling in January 2019 which cleared Sun of any wrongdoing.

Under the shadow of the controversy, Sun competed at July's world championships in South Korea, where he won gold in the 200 and 400 free to take his long-course title total to 11 since his worlds debut in 2009.

During the meet, some foreign rivals, led by Australia's Mack Horton, who beat Sun to 400 gold at Rio 2016, snubbed the Chinese star by refusing to join him on the podium or shake his hand.

Despite Sun's close call at the Shenzhen Universiade Natatorium, there were plenty of other Chinese victories for the home fans to cheer.

The host bagged five golds on day one of the FINA series, with two-time world champion Xu Jiayu winning the men's 100m backstroke (53.01) and world-record holder Liu Xiang storming to victory in the women's 50m backstroke (27.36).

The 2020 season-opening circuit heads to Beijing for its second leg this weekend.