Vice President Joe Biden, whose 2016 presidential ambitions have been overshadowed by former Secretary of State Hillary Clinton's air of inevitability, finally got a chance to show some foreign policy gravitas on a trip to China.

Beijing’s recent declaration of an air defense zone in the East China Sea was an unexpected move and sparked a new flashpoint in U.S.-Sino relations. The zone imposes restrictions on flights in an airspace that covers contested islands and waters also claimed by key U.S. allies Japan and South Korea.

Biden had a previously scheduled trip to the region, and President Obama didn't hesitate to put him on the hot seat when the diplomatic imbroglio broke. Biden faced the tricky task of not angering China while also reassuring U.S. allies in the region.

China has long claimed sovereignty over the East and South China seas, which are thought to contain rich oil and gas deposits, and setting up the new air defense zone only heightened hostilities with several regional neighbors. Japan, South Korea, Malaysia, the Philippines, Taiwan and Vietnam all are trying to push back against China's dominance in Asia and its control of air and maritime space.

The situation was extremely precarious when Biden began five hours of face-to-face talks with Chinese President Xi Jinping. The U.S. initially challenged the Chinese by flying B-52 bombers through the zone without first notifying Beijing.

Once in the country, however, Biden tried to cool the overheated atmosphere, telling the Chinese: “We've got to unwind this tension.”

Although Biden pressed the point that the U.S. “doesn't recognize” the zone over the East China Sea, he also tried to persuade China to agree to establish a system of emergency communications that would connect Beijing to leaders in Japan and other countries to avoid misunderstandings that could spark conflict.

Xi laid out China's point of view on the matter and said only that he would “take on board” Biden's suggestions.

The administration didn't expect the Chinese to immediately abolish the new zone, U.S. officials said afterward. Biden's goal was simply to urge restraint and demonstrate that Washington takes the matter very seriously.

Biden also managed to quietly press for human rights in China, meeting with foreign reporters whose access has been blocked by Beijing.

In Biden, Obama had an experienced hand to massage U.S.-China relations through this tense period.

The former Senate Foreign Relations Committee chairman has a long relationship with Xi, and his voice was one that the Chinese president could not ignore at this critical point.