No diplomatic ties existed between the countries, just intermittent embassy- level contacts in places like Warsaw and Geneva - until Winston Lord found himself on a Pakistani aircraft in July 1971, accompanying his boss, Henry Kissinger, on a super-secret trip to Peking.
The China visit everyone remembers today is President Nixon's "Journey for Peace" that began 25 years ago today. But that truly historic encounter would have been impossible without the Kissinger mission, born of the interest of Washington and Peking in thwarting the ambitions of their common rival, the Soviet Union. The tectonic plates of global diplomacy moved as a result.
"It was very dramatic, flying past the Himalayas and K-2, then arriving in Peking in the middle of the night," Mr Lord said. "As we approached Chinese airspace I went to the front of the plane so I could claim to be the first American official into Chinese territory since the revolution. Henry, of course, was first off the plane when we landed. For some reason, he hadn't taken enough shirts, and was ranting and raving about it. Eventually he borrowed one, but it was too big and had the label 'made in Taiwan'. I remember making a joke to Henry about it, 'You've lost your shirt to the Chinese already'."
The summit six months later needed little such improvisation. Its rationale was obvious. "Clearly the Communist world was no longer to be seen as a single bloc. Relations with China, we reckoned, would give us leverage with the Soviet Union - and they did. Within months, even weeks, relations with Moscow improved greatly. We also hoped to use Russian and Chinese influence to end the war in Vietnam," Mr Lord said.
And even deeper considerations weighed too. "We knew that at some point a country with a quarter of the world's population was going to matter. There were things in it for both sides. China was vulnerable then ... Ties with us would would help them break their isolation, build contacts with Japan and get them into the UN."
Even though China and the US did not exchange ambassadors until 1979, the summit in effect codified Sino-American relations. Its main fruit was the document known as the "Shanghai Communique".
It began with a long section setting out the countries' differing views on major issues. "The Chinese wanted this," Mr Lord said. "They argued that if we made clear our disagreements, it would make the rest of the communique more credible. And 25 years later, it is still constantly referred to, as the bedrock document between us."
For Richard Nixon, it was the crowning moment of a presidency that 30 months later would end in disgrace.
Much has changed in the quarter century since, during which Mr Lord served as US Ambassador to Peking from 1985 to 1989, and as Assistant Secretary of State for East Asian affairs during President Clinton's first term. "For one thing the Chinese are much stronger. The economy is surging, they are a growing military power. The leadership context is different too ... Today it's more of a collective leadership. Jiang Zemin is in charge, but clearly there's less flexibility. They have to work out a consensus which makes things more difficult, and after Deng's death there's bound to be jockeying ...."
But Mr Lord argues that in their different ways, both sides need each other. "We account for one-third of Chinese exports, they have a $40bn [pounds 25bn] trade surplus with us and they want access to US technology. Also despite Taiwan, Hong Kong, human rights, arms and nuclear sales, and all the rest, the American presence in East Asia is not entirely unwelcome to them, if only as a balancing force against any resurgence in Japanese militarism."