Aquino's meeting with Murad Ebrahim, chairman of the Moro Islamic Liberation Front (MILF) in Tokyo on Thursday changed the minds of rebel leaders who had become sceptical of the talks, said MILF vice-chairman Ghadzali Jaafar.
"There were members of the central committee who were doubtful about the sincerity and seriousness of the Aquino administration before the meeting," Jaafar told reporters in a telephone interview on Sunday.
"But these talks were like an injection that gave new hope to the leaders for the peace talks," Jaafar said.
However Jaafar warned the political opposition might find a reason to oppose a settlement before Aquino's term ends in 2016.
The head of opposition legislators on Sunday questioned the secrecy of Aquino's surprise meeting with Murad.
"Secrets may be maintained between lovers, but there should be no secrets between the president and the Filipino people," House minority leader Edcel Lagman said in a statement.
He said Aquino should say why the meeting was kept a secret and reveal the "bottom line demands" of the MILF.
Other political figures have also expressed concern over Aquino's meeting with the leader of the MILF whose three-decade long rebellion has killed more than 150,000 people.
The 12,000-strong MILF had initially aimed for an independent Muslim state in the mostly Catholic country's southern island of Mindanao, but is now focused on autonomy.
The 14 years of on-off negotiations with the government have been frequently marred by violence and distrust of the Muslim group.
There was widespread anger after Aquino's predecessor, president Gloria Arroyo offered the MILF a proposed peace deal in 2008 that would have given them control over vast tracts of land.
The Supreme Court rejected the plan and in response rogue MILF commanders launched attacks on communities in Mindanao that left about 400 people dead and displaced more than 750,000.
Aquino spokeswoman Abigail Valte said in a radio interview that most people welcomed the president's unprecedented move to speed up the talks.
"By far, we have seen that the reactions of our countrymen have been positive, especially among the stakeholders in Mindanao," Valte said.