Divisions and pressure from the international community pushed the National Super Alliance to seek redress from the Supreme Court after the presidential election loss, it has emerged.
Sources said coalition leader Raila Odinga and senators James Orengo (Siaya) and Johnson Muthama (Machakos) were for mass protests.
"The three insisted that the Supreme Court legitimised a dirty election in 2013 and they saw nothing different this time round," an insider told the Nation Thursday.
Mr Odinga's running mate and Wiper party leader Kalonzo Musyoka, Amani National Congress' Musalia Mudavadi, Bomet Governor Isaac Ruto of Chama Cha Mashinani, Ford-K leader Moses Wetang'ula and members of the technical team opposed street protests.
There was already an internal rebellion when Nasa Ukambani wing under Makueni Governor Kivutha Kibwana openly rejected the idea of street protests and warned Mr Musyoka against taking that path.
The county boss has emerged as one of Mr Musyoka's most trusted ally.
This led to the fallout with Mr Muthama. The fact that the senator was in support of mass action meant that Mr Musyoka was isolated and could only listen to Prof Kibwana.
It is during the scrutiny of forms 34A and 34B that confidence levels in the technical team grew.
The committee said sufficient evidence had been gathered to build and sustain a case against the declaration by Independent Electoral and Boundaries Commission of Mr Uhuru Kenyatta as winner of the presidential election.
According to the source, Nasa sought the services of electoral forensic and handwriting experts to plough through the thousands of forms to determine their validity and if there was foul play on the part of the IEBC.
"Initially, we were opposed to the legal process but our confidence levels rose when we came face to face with the glaring mess in the forms," the source said.
Among the issues said to have softened Mr Odinga's heart was when the audit team said many forms 34A posted on the IEBC portal from some counties did not bear the commission's stamp as required by the law.
But it was the international community that put paid to any hopes that Mr Odinga would use justify the street protests.
A Nasa insider told the Nation that the United Kingdom, the United States and the European Union piled pressure on Mr Odinga to either concede defeat or file a petition at the Supreme Court.
"There were several direct and indirect meetings with the ambassadors of the UK, the US and the European Union," the source said.
On Thursday, EU Election Observation Mission head Marietje Schaake confirmed having held meetings with the opposition chiefs but refused to divulge details.
"I have had conversations with the Nasa leadership and Mr Odinga. We talked about many things," she said.
However, she insisted that she been on record and clear that "the rule of law should be respected, and the courts are the avenue to take to seek redress or challenge the process and outcome of the elections".
Ms Schaake said the mission had consistently called for transparency but expressed concern that it took long for the forms to be uploaded online.
"We are glad the forms are online. Anyone can challenge the process or the results," Ms Schaake said.
"The mission will be looking in detail at the entire process and will comment elaborately in our final report.
"We will also be closely following the petitions. The courts are the place for justice, and we will be looking to see how they do their job."
While delivering his long awaited speech on Wednesday, Mr Odinga said the clampdown on the Africa Centre for Open Governance and the Kenya Human Rights Commission motivated Nasa to make a U-turn and challenge the presidential election results in court.
He said the clampdown showed the government's determination to silence voices that could seek legal redress.
Sources inside the six-hour meeting on Monday told the Nation that the UK and US attempted to prevail upon the Mr Odinga to concede defeat but he flatly rejected the idea.
He is said to have been angry with the rush by the international observers to validate the elections "in the face of glaring anomalies witnessed in the transmission of results".
"He was shocked by the haste with which everybody went about congratulating the commission for a job well done and asking him to seek legal redress if he was not satisfied.
"Mr Odinga was particular angry with the stance adopted by observers, which suggested that elections were just about announcing the winner," the source said.
"Mr Odinga was shocked by the avalanche of opposition he was getting.
"It was like he was being condemned for losing even when the infamy of result transmission was unfolding before everybody's eyes."