Hong Kong (CNN) Manila and Beijing are to hold direct talks on the South China Sea for the first time Friday, a move that may strengthen Beijing's hand in the festering dispute.

By agreeing to bilateral negotiations, analysts say the Philippines weakens the position of other countries involved, impedes efforts for a multilateral solution, and lays bare China's ability to control the agenda in the South China Sea and US unwillingness to antagonize Beijing over the dispute.

"China is winning the argument here and others will have to move accordingly," says Mathew Davies, head of the International Relations Department at the Australian National University, who specializes in Southeast Asian politics.

A crucial shipping route, the South China Sea is home to a messy territorial dispute pitting China, Taiwan, Vietnam, the Philippines, Brunei and Malaysia against one another.

So what's changed?

But under President Rodrigo Duterte, who took office in June 2016, the Philippines has pivoted toward Beijing -- seeing China as a source of much needed investment -- and away from the US, which, despite a mutual defense treaty, Duterte regards as an unreliable ally.

Chito Santa Romana, Philippine Ambassador to China, says that Manila didn't get the assurances it wanted from the US and the international community that they would support the Philippines in any conflict with China over the South China Sea.

"That is why the president kept asking the US ambassador, 'are you with us or not?' He did not get a clear answer," he told CNN in an interview. "The strategic logic is very simple. Don't put your eggs in one basket."

In a statement, a US State Department spokesperson told CNN that its alliance with the Philippines is "ironclad."

Just this week, China and the Philippines inked a $72 million grant on social and economic planning. It comes off the back of substantially larger promises of Chinese investment.

Santa Romana denied the Philippines had sold its sovereignty on the South China Sea to secure investment from China.

"The Philippines under Duterte decided that we had to address the overdependence on one major power whose capital is thousands of miles away and to pay attention to our neighborhood, particularly, to the biggest neighbor we have -- that is China," Santa Romana said.

The shift by the Philippines has gathered speed under an unpredictable new White House, said Davies. US President Donald Trump has eased up on Beijing over the South China Sea -- a decision that may be linked to efforts to enlist China's help in reining in North Korea.

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Code of conduct

Before Friday's talks, ASEAN, a regional grouping of Southeast Asian nations, had been working toward a multilateral solution -- primarily through negotiating a code of conduct. Beijing had long advocated a bilateral approach.

"Before there was a superpower underpinning ASEAN, which made it a more difficult strategic calculus for China to play," says Davies.

"Now, as the US pulls back, the weakness of Southeast Asian nations is exposed. China can work bilaterally and with ASEAN to get its message across."

Bilateral meetings make it easier for China to "maximize and cement" its position in the South China Sea, he added.

"They are weak countries but there was strength in numbers."

Red line?

The Philippines is likely to seek a permanent freeze on China's activities in the South China Sea, according to Zhang Baohui, a professor of political science at Hong Kong's Lingnan University -- something that would legitimize the roots China has put down there.

Beijing has reclaimed more than 3,000 acres in the Spratly Islands since early 2014, turning sandbars into military bases equipped with air fields and weapons bases. It has controlled the Paracel islands further west since 1974.

What Manila doesn't want to see is China build on Scarborough Shoal -- a small but strategic reef and fertile fishing ground 200 kilometers (130 miles) west from the Philippine island of Luzon.

However, he thinks it's unlikely China will pursue this given its successful and largely uncontested build up in the Spratlys -- at least for now.

"I think China understands that Duterte has changed the whole dynamic in the South China Sea in their favor. If they're smart, they won't press further," he says.