He made clear that he's serious about his vows to wring a new deal from China on trade and appears to be ready to challenge at least the atmospherics of the US relationship with Taiwan -- an issue of deep sensitivity in Beijing.
His tactics also show that President Trump promises to be just as much of a disruptor in international relations as he has been in domestic politics, no matter what conventions get broken in the process.
But so far, analysts say, it is not clear that Trump -- for all his bombast -- is preparing to tear up the strategic framework that has underpinned Sino-US relations since President Richard Nixon went to China to open relations between the two countries four decades ago.
Trump's inexperience in foreign affairs and the fact that he is yet to name a secretary of state or senior Asia policy team means there is uncertainty in Washington and across the Pacific about his intentions.
China watchers are trying to work out if the call with Tsai is a sign that Trump is ready to challenge the strategic ambiguity of the "One China" policy itself that has been the cornerstone of bilateral relations since the establishment of diplomatic relations.
The formula, enshrined in the documents that eventually led to the establishment of US relations with China, permits Beijing to regard Taiwan as a part of China and the United States to sell the nationalist island arms to defend itself against the mainland, and has headed off a major US-China clash over the issue.
Trump's call with Tsai was initially described by the presidential transition as a courtesy call. But now his supporters suggest that the first reported direct contact between a president or a president-elect with a Taiwanese leader in 40 years was more significant.
"Taiwan is our ally," former Trump economic adviser Stephen Moore said in a radio interview Monday on the Big John and Ray Show on WLS AM890. "That is a country that we have backed because they believe in freedom. We ought to back our ally, and if China doesn't like it, screw 'em."
Reince Priebus, Trump's pick to be his chief of staff, said Monday that Moore is not an adviser for Trump's transition.
But the diplomatic balance over Taiwan is so delicate that some analysts fear Trump could be starting a confrontation that could easily spin out of control, endanger other crucial areas of the US-China relationship and even so hike tensions that a military clash is possible in the Pacific.
"I think that until the inauguration, China is unlikely to let this escalate with the President-elect," said Jessica Chen Weiss, a China expert at Cornell University."After January 20, I think all bets are off."
"China would be willing to sacrifice cooperation across the board to stand firm against any move to give Taiwan diplomatic recognition and undermine the "One China policy," according to Weiss.
What is Trump's strategy?
When news broke of Trump's conversation Friday with Tsai, many foreign policy experts simply chalked it up to a rookie error.
But after Trump hit back on Twitter by pointing out the seemingly illogical convention that will give him power as president to sell arms to Taiwan but not talk to its leader, the consensus began to shift.
When Trump returned to Twitter over the weekend to accuse China of devaluing its currency and building a "massive military complex" in the South China Sea, it became clear that he was making a tough initial gambit in his unfolding relationship with Chinese President Xi Jinping.
"He wants to negotiate a new deal with China. Obviously this call does what he said he is going to do. He wants to shake up China," said Michael Pillsbury, an author and China expert who has advised Trump and called him a "strategic genius."
"He is going to be firm and he is reminding them we need to have a talk now (between) Beijing and Washington," Pillsbury said on CNN Monday.
Trump's attitude mirrors a recent Foreign Policy article written by two other advisers -- Peter Navarro and Alexander Gray -- that was seen widely as a blueprint for his upcoming China strategy.
The authors warned that President Barack Obama's Asia pivot, partly conceived to cope with the rise of China, was a case of talking loudly but "carrying a small stick."
Trump, they suggested, would adopt a policy of "peace through strength," vastly expanding the US Navy to respond more robustly to Chinese territorial claims in the East and South China Seas and make clear that American interests in the region would be paramount.
Patrick Cronin, a senior director at the Center for A New American Security, said that Trump was intent on demonstrating to China that its rising power would not be met by an atrophying United States.
"What Trump is doing is to try to create new leverage, new maneuvering room in what is going to be a protracted complex negotiating position with China," said Cronin, who backed Democratic nominee Hillary Clinton in the presidential race. "This move signals early on that he is capable of coloring outside the lines on US-China relations, not just in domestic policy. "
Some commentators have argued that China sees Trump's presidency as an opportunity. His decision to cancel the Trans-Pacific Partnership trade deal is seen as playing into Beijing's hopes of establishing its own economic order in the region, since the massive US-led trade deal cut out the Asian superpower.
Trump's campaign trail warnings that Japan and South Korea must do more to pay for their US defense umbrella were also interpreted as presaging a US retreat from the region.
But China might be taking another look at Trump after this weekend.
Beijing's initial response to Trump's call with Tsai was sophisticated -- restating the importance of the "One China policy" but also giving Trump and his team the benefit of the doubt by blaming Taiwan for initiating the call.
Such a strategy suggests that Beijing could expect that the new US president will initially have a contentious relationship with China -- as has happened in the past -- before the logic of the wider relationship eases tensions.
Former Australian Prime Minister Kevin Rudd, a longtime China-watcher, said Beijing had made a decision not to play into Trump's hands.
"I think we are in for at least a couple of months of general uncertainty," Rudd told CNN's Richard Quest on Monday.
"The Chinese response still is this is a shake-down period -- perhaps President Trump is pushing us and probing us. Perhaps he is seeking to obtain some negotiating chips," he suggested they're saying, "but we are not going to rise to the bait."
However, Beijing also sent clear signs -- through a Global Times editorial, often a conduit for Communist Party thought -- that if Trump was spoiling for a fight, he could be biting off more than he can chew.
"No matter what the reasons are behind Trump's outrageous remarks, it appears inevitable that Sino-US ties will witness more troubles in his early time in the White House than any other predecessor," the Times said. "We must be fully prepared, both mentally and physically, for this scenario."
If it comes to it, China could make life difficult for the Trump administration.
It could refuse to help slow the nuclear program of close ally North Korea, impose tariffs on US goods or make it more difficult for American businesses to operate in China. Weiss said Beijing could also hold military maneuvers to show the US and Taipei "that China's resolve is unshaken."
Trump's critics are puzzled why he would open his relationship with China by initiating a clash over Taiwan and then doubling down.
"Some of the progress we have made in our relationship with China could be undermined by this issue flaring up," White House spokesman Josh Earnest warned.
Christopher Hill, a former assistant secretary of state, said that the "One China" policy was successful and did not need fixing.
"It's not an issue, it works, it is not among the list of the terrible problems in East Asia," Hill told CNN International's Hala Gorani.
"If we start going after things that are not a problem, I think that some of these problems that we have for which we need US-China cooperation, if you will, we are going to find it tougher and tougher to work with the Chinese," he continued.
No consensus in Washington
Still, there is no consensus in Washington that Trump really wants to throw the foundations of US-China policy out the window.
Walter Lohman, a former Republican Senate policy aide who is now director of Asian Studies at the Heritage Foundation, said that both sides remain committed to the basic post-Nixon era framework of US-China relations.
"I could see tensions increasing, but all within the framework," he said. "They definitely want to preserve it, and I think right now, they are calculating that we want to do the same."
Republican Rep. Matt Salmon, chairman of the House Foreign Affairs subcommittee on Asia and the Pacific once lived in Taiwan and has been to China more than 50 times, and said he saw no risk to the "One China Policy."
Asked on CNN whether Taiwan could cause a military clash between the US and China, he added: "Not at all."
"I think that the Chinese understand how important we are to their economic success," Salmon said on CNN.
Despite the uproar, it's too early to panic about the state of US-China relations under Trump, according to Rudd.
"Let's not proclaim cataclysm on the basis of a tweet or two, or four or six," he said.
UPDATE: This story has been updated to reflect that Moore is not an adviser on the transition.