It turned out to be the international crisis that wasn't.
Less than a day after 10 US Navy sailors were detained in Iran when their boats drifted into Iranian waters, they and their vessels were back safely with the American fleet.
US Secretary of State John Kerry tapped the personal relationship he has formed with Iranian Foreign Minister Mohammed Javad Zarif in the three years of negotiations over Iran's nuclear program, speaking with him at least five times by telephone.
US Defense Secretary Ash Carter thanked Kerry after the sailors' release and couched the incident in humanitarian terms, noting that "the US Navy routinely provides assistance to foreign sailors in distress".
For Tehran, the Americans' swift release was a way to neutralise a potential new flashpoint days before it was expected to meet the terms of last (northern) summer's nuclear deal, which will give Iran significant relief from painful economic sanctions.
The nine men and one woman were detained on Tuesday after at least one of their boats suffered mechanical problems off of Farsi Island, in the middle of the Persian Gulf, which has been used as a base by the Revolutionary Guard speedboats since the 1980s.
The Americans' small Riverine boats were sailing between Kuwait and Bahrain on a training mission when the US lost contact.
The sailors left the island at 1943 AEDT on Wednesday aboard their boats, the US navy said. They were picked up by navy aircraft, and other sailors took control of the vessels for the return voyage to Bahrain, where the US 5th Fleet is based.
Commander Kevin Stephens, a 5th Fleet spokesman, said the priority now would be determining "how exactly these sailors found themselves in Iran".
A senior defence official said they were being debriefed and getting medical exams at a US medical facility in Qatar but were unharmed.
The Revolutionary Guard released images of the US sailors before their release, showing them sitting on the floor of a room. They looked mostly bored or annoyed, although one appeared to be smiling. The woman had her hair covered by a brown cloth. The pictures also showed what appeared to be their two boats.
State TV later released more video and photos of the Americans apparently surrendering on their knees, their hands behind their head. It also showed machine guns and ammunition they had onboard.
"After determining that their entry into Iran's territorial waters was not intentional, and their apology, the detained American sailors were released in international waters," the Guard said.
Vice President Joe Biden, speaking later to CBS This Morning, denied the US made an apology.
"There's nothing to apologise for," Biden said. "When you have a problem with the boat, you apologise the boat had a problem? No, and there was no looking for any apology. This was just standard nautical practice."
Iranian TV ran video of one of the sailors apologising for the intrusion into Iranian waters.
"It was a mistake. That was our fault and we apologise for our mistake," the unidentified sailor is shown saying in English.
The US Central Command later said: "The video appears to be authentic, but we cannot speak to the conditions of the situation or what the crew was experiencing at the time."
It added that the crew was undergoing "the reintegration process and we will continue to investigate this incident.
"What matters most right now, however, is that our sailors are back safely."
Iranian state television has released footage of a detained US sailor apologising for his patrol boat having entered Iranian territorial waters in the Gulf by mistake.
"It was a mistake, that was our fault, and we apologise for our mistake," the sailor, who was introduced as a US navy commander, said in English on IRIB state TV on Wednesday.
"My navigation system showed I was in Iranian waters but I made a mistake and entered," the television quoted him as also saying.
All 10 detained sailors were released by Iran on Wednesday morning after being held overnight, quickly ending an incident that rattled nerves days ahead of the expected implementation of a landmark nuclear accord between Iran and world powers.