President Barack Obama, who a day earlier was the surprise winner of the Nobel Peace Prize, telephoned Clinton in Switzerland to congratulate her on overcoming a last minute-hitch that threatened to scuttle the Turkish-Armenian deals, a senior State Department official said.
Clinton was headed to the airport in the Swiss city of Zurich following an intense and frantic day of negotiations when she got the call from Obama, the official said. The official spoke on condition of anonymity because the call was private.
"He was very excited, he felt like this was a big step forward and wanted to check in," the official told reporters aboard Clinton's plane as she flew from Zurich to London, the second leg of a five-day tour of Europe and Russia. "He called to congratulate her and the team."
"We had a good night in Zurich," Clinton said on the plane.
For several tense hours in overcast Zurich, however, that was anything but a sure thing.
Having come merely to witness Saturday's signing, Clinton instead became embroiled in a dramatic turn of events that began when both sides balked at signing agreements on establishing diplomatic relations and opening their sealed border after a century of enmity.
Both had objections to language in statements the side wanted to read after signing the deals, concerns that burst into the open just minutes before the ceremony was to begin at the University of Zurich in the shadow of Switzerland's snowcapped Alps.
Clinton's motorcade had just arrived at the venue when it abruptly turned around and returned to the luxury hotel where she had met separately earlier with Turkish Foreign Minister Ahmet Davutoglu and Armenian Foreign Minister Edward Nalbandian.
There she spoke by phone from the sedan in the parking lot, three times with the Armenians and four times with the Turks. At one point, a Swiss police car, lights and siren blazing, brought a new draft of the Turkish statement from the university to the hotel for review.
After nearly two hours, Clinton and Armenian Foreign Minister Edward Nalbandian met in person at the hotel and drove back to the university where negotiations continued in the presence of Swiss and European mediators and the foreign ministers of Russia and France.
About an hour later, Clinton and the others brokered a compromise under which no statements would be read at the ceremony.
She said she had repeatedly impressed on the Turks and the Armenians that the agreements, known as protocols, that had been negotiated over months were too important not to be signed now. The protocols, she said, should speak for themselves without additional statements.
"We just kept making our points," she said, referring to herself and the top U.S. diplomat for Europe, Philip Gordon. "This needed to be done."
"It's just what you sign up for," Clinton said of her role."When you are trying to help people resolve long-standing problems between themselves, it is a very challenging process."
To take effect the agreements must be ratified by the Turkish and Armenian parliaments and face stiff opposition in both countries, which have a particularly bloody history.
The contentious issue of whether the killing of up to 1.5 million Armenians during the final days of the Ottoman Empire amounts to genocide is only hinted at in the agreement as is the matter of the disputed Armenian-occupied enclave of Nagorno-Karabakh in Azerbaijan.
Turks have close cultural and linguistic ties with Azerbaijan, which is pressing Turkey for help in recovering its land. Turkey shut its border with Armenia to protest Armenia's 1993 invasion of the territory.