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BEIJING — Thousands of riot police were deployed for a soccer showdown Thursday night that was more than the average grudge match.

China soccer fans celebrate their team's 1-0 win over South Korea in the 2018 World Cup qualifier on Thursday. Color China Photo / via AP

The World Cup qualifying game in Changsha pitted hosts China against South Korea. It also whipped up Chinese nationalist sentiment at a time of high political tension over the rollout of a U.S.-made missile defense system in Asia.

Officials were so worried about clashes that the Hunan provincial sports administration urged fans to show “rational patriotism” to avoid trouble.

To ensure that, a 10,000-strong security force was deployed to watch over the capacity crowd of 55,000.

Dozens of trucks carrying paramilitary and riot police were stationed around the stadium.

Chinese fans were given free red T-shirts with the slogan “Changsha War” in Chinese characters.

In the sea of red, only around 150 South Korean supporters were in the 250 seats designated and guarded for them.

Police (seen top) sit behind South Korean fans during the World Cup qualifer against China on Thursday. GREG BAKER / AFP - Getty Images

The event illustrated the extent to which China’s relationship with South Korea has deteriorated since the first components of the Terminal High Altitude Area Defence, or THAAD, anti-missile system arrived to the region earlier this month.

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THAAD is designed to protect U.S.-ally South Korea and American bases there from the growing threat of North Korea’s weapons programs.

Kim Jong Un's regime has stepped up testing of its missiles as a protest of the U.S. joint military drills with South Korea, and there is concern preparations for a sixth nuclear test are underway.

China is fiercely opposed to THAAD, arguing a system to intercept short-and-intermediate range ballistic missiles installed so close to North Korea’s launch sites will only serve to undercut China’s strategic defenses.

The longer term concern for China’s military: If THAAD expands to Japan, it creates a common operating picture for U.S. allies in Asia.

“Even if North Korea collapses, missile defencs would not go away,” a former U.S. national security adviser told NBC News. “The worry [for China] is that THAAD is a basis for a collective security system… that does not include China.”

THAAD was among the issues on the agenda during Secretary of State Rex Tillerson’s recent visit to Asia.

Experts stress that THAAD is a major concern for China’s government.

The issue has stoked nationalist fervor in China, and triggered an anti-South Korean backlash with state media urging a boycott.

"Some critics in the West have said that China, as a country under the rule of law, has no reason to punish South Korean enterprises that are doing businesses in the Chinese market," a Global Times op-ed published earlier this month read. "However, all states have the right to sanction those that have posed a threat to their national sovereignty and strategic security interests."

Some Chinese travel companies have already stopped booking tours there, causing a drop in crucial tourism business.

China's Yu Dabao and South Korea's Jang Hyunsoo in action during a World Cup qualifier on Thursday. CHINA STRINGER NETWORK / Reuters

China has also blocked streaming of popular South Korean television shows and soap operas, and K-pop stars have cancelled concerts on the mainland because of problems getting travel visas.

Across China, there have been protests at outlets of Lotte Group, the South Korean retail giant that gave up its golf course as a THAAD deployment site.

A few days after it agreed to the deal, a cyberattack took down its online shopping sites. Other Lotte stores have been mysteriously closed by Chinese authorities for various municipal infractions.

Officially, China hopes it can pressure Seoul to reconsider.

The snap election in May could bring the country’s opposition Democratic Party to power. Its leader Moon Jae-in has expressed reservations about hosting an anti-missile system that might reinforce South Korea as a North Korean target.

Chinese fans hold national flags during a World Cup qualifier against South Korea on Thursday. CHINA STRINGER NETWORK / Reuters

The regional rivalry came to a head on the soccer field, in the city where Mao Zedong, the late Communist leader and founder of modern China, started his political career.

The sheer size of the security force showed that authorities had no tolerance for violence, even if nationalist protests had been allowed in the past.

In the end, China won the game, 1-0. The only commotion: cheering by surprised Chinese fans who became more distracted by the World Cup qualifier than global affairs.