Ousted Honduran president Manuel Zelaya appeared first, and left shortly before the arrival of the man who replaced him after a military coup, his former friend and political ally Roberto Micheletti.
If Zelaya offered any concessions, he wasn't talking about them. As he headed back to his hotel, Zelaya called for "the reestablishment of the state of law, democracy and the return of the president elected by the Honduran people."
Micheletti, for his part, insists that Zelaya must relinquish any claim to the presidency.
Each side was naming four representatives to keep meeting, and if that effort produces results, a face-to-face encounter was possible.
"Positions begin to soften" once two sides start talking, Arias said hopefully before the mediation sessions began.
Even getting both sides to appear in the same city was an achievement something that hasn't happened since the leftist Zelaya surrendered under gunfire and was flown out of his country by masked soldiers on June 28.
This coup crisis has become one of the biggest tests so far for the Obama administration in Latin America.
Arias who won his Nobel for helping Central Americans resolve their civil wars was invited to mediate by U.S. Secretary of State Hillary Clinton. That move effectively sidelined Venezuelan President Hugo Chavez, who had lent Zelaya a Venezuelan plane and other support, and cast the crisis as an epic battle between the poor and the region's "oligarchies."
President Barack Obama has framed the issue in non-ideological terms, encouraging leaders from the left and right to come together to support the institutions of democracy.
Obama has insisted that Zelaya be restored to power, but "not because we agree with him," he told an audience in Russia. "We do so because we respect the universal principle that people should choose their own leaders, whether they are leaders we agree with or not."
U.S. State Department spokesman Ian Kelly said no U.S. representatives were participating in the mediation sessions. "We are keenly interested in these talks. We want to see a good outcome that restores the democratic order in Honduras. But I just want to emphasize, this is President Arias', these are his talks."
In Honduras on Thursday, thousands of Zelaya's supporters and detractors continued marching in the streets. Pro-Zelaya forces cut off several highways, including a key southern truck route to Nicaragua and El Salvador. Backers of the Micheletti government demonstrated in the northern industrial city of San Pedro Sula and other places.
In contrast, very few people almost all journalists showed up at the metal security gates placed in front of Arias' home, a one-story house in a residential neighborhood of San Jose. The only guards were about two dozen unarmed tourism police wearing polo shirts.
Both Zelaya and Micheletti have said there is nothing to negotiate that the other man can't possibly be president of Honduras. Oscar Arias also sought to dampen expectations, saying before the talks that "in two days there could be a solution or it could be that in two months there is no solution."
And Micheletti did express some optimism after his plane touched down. "We will work ceaselessly to find a successful solution to the present situation," Micheletti said, committing to "trying to solve my country's internal differences in a peaceful way."
Micheletti, a congressional leader who was named president by legislators following the coup, has already replaced his foreign minister, who caused a flap by repeatedly referring to Obama as "a little black man" and a "little black field hand."
Enrique Ortez, now replaced by Honduras' former ambassador in Washington, Roberto Flores, has been a prominent spokesman for Micheletti, arguing that the coup was legal because congress and the Supreme Court had ruled Zelaya was illegally pursuing a referendum to change the constitution.
The world has rallied behind Zelaya. The United Nations and the Organization of American States also have demanded he be returned to power, imposing or threatening sanctions and aid cuts. Venezuela said it is canceling shipments of subsidized oil, and the U.S. suspended more than $18 million in military assistance and development aid programs. No other country has recognized the interim administration.
But support for Zelaya is much less certain inside the impoverished country.
Some Zelaya supporters claim Honduras' wealthy class backed the military action because Zelaya raised the minimum wage and pushed other policies that favor the poor. Micheletti counters that Zelaya and Chavez stoked class divisions.
Before the talks began, Zelaya offered to drop his aspirations for a constitutional change that might allow him to run for another term.