It was exactly half a century ago, but former Chinese table tennis champion Zhang Xielin still vividly remembers how a shaggy-haired American table tennis player stepped onto the Chinese team's bus, a chance encounter that would eventually shape history.

It was the world championships in Nagoya, Japan, and Glenn Cowan mistakenly hopped in with Zhang and his teammates – an awkward moment because the United States and China were then deeply at odds.

"We were on the bus and were talking and laughing," Zhang, now 80, told Agence France-Presse (AFP).

"But when we realized that an American had come onto the bus, we fell silent."

The Chinese triple world champion Zhuang Zedong eventually came forward and famously broke the ice, giving Cowan a silk embroidery as a souvenir from China.

They did not know it at the time, but it was the spark for China and the United States to begin normalizing relations, in what became known as Ping Pong Diplomacy.

Zhang, a doubles world champion and later China's coach, recalled: "Mr. Zhuang understood that there was a difference between the American people and the American government and that we should be nice to American people, so he took the initiative to chat with Glenn."

Photographers captured Zhuang and a 19-year-old Cowan shaking hands and smiling.

"The newspaper came out the next day and it seemed that China and the United States were about to have a relationship," said Zhang.

Days later, on April 10, 1971, the U.S. team became the first Americans to step foot in China for nearly a quarter of a century when they were invited to play friendly matches in the country.

The thaw saw President Richard Nixon visit China in February 1972, and a Chinese table tennis squad visit the U.S.

In 1979 formal relations were established between the two countries.

'Compete peacefully'

Yao Zhenxu played Cowan, who died in 2004, during the Americans' groundbreaking trip.

Yao still remembers the score, he won 21-12, 21-14, and says that Cowan thanked him afterward for "a serious game."

The American team was vastly inferior to the Chinese, so the hosts sometimes let their visitors win points in the spirit of sportsmanship and goodwill.

Now 74, Yao says that it was only afterward that he realized that he had played a part in something historic.

"Because of Ping Pong Diplomacy we changed the world order, and the people of China and the United States started friendly exchanges," he said.

Yao appeared alongside Zhang in Shanghai on Saturday to mark 50 years of ping-pong diplomacy, with the city authorities hosting an event with speeches and friendly amateur matches.

However, the anniversary comes at a time when relations between Washington and Beijing have deteriorated markedly over several issues, notably trade, the fate of China's Uyghur minority and a clampdown in Hong Kong.

In a recorded speech to mark the 50th anniversary, China's ambassador in Washington, Cui Tiankai, accused some in the U.S. of "ideological bias and zero-sum thinking."

But he and Chinese state media took a largely positive tone, with Xinhua news agency hailing Ping Png Diplomacy's "wonderful legacy."

Yao and Zhang hope that the spirit of 1971 can help shape future relations between the world's top two economies for the better.

"Everyone knows that China and the United States' relationship is a bit tense nowadays," said Yao.

"We hope that we can agree to disagree and keep friendly relations.

"Don't be afraid of competition, we can compete peacefully."