Election monitors from the European Union say they found no irregularities in last Sunday's hotly disputed presidential election.
Supporters of Felipe Calderon have been celebrating
The EU said its 80 monitors nationwide did not witness any wrongdoing.
Andres Manuel Lopez Obrador has vowed to launch protests after the razor-thin victory of his rival Felipe Calderon.
But Mr Calderon has already begun to spell out his policies and has taken congratulatory calls from overseas leaders, including US President Bush.
The final tally from the election showed that just a few hundred thousand votes separated the two candidates.
Conservative candidate Mr Calderon finished with 35.88%, against 35.31% for Mr Lopez Obrador, the candidate of the Party of the Democratic Revolution (PRD).
The European Union monitoring team said its monitors "did not report any incidents or irregularities that could have affected the transparency of the counting process and that could have impacted the results".
Mr Calderon, of the ruling National Action Party (PAN), on Friday began to set out his policies, including support for US immigration reforms.
He also pledged to close the wealth gap between rich and poor and aid Mexican farmers.
Mr Calderon took calls of congratulations from Canada, Spain and US President George W Bush.
Mr Bush's spokesman, Tony Snow, said the president had called to tell Mr Calderon he "looked forward to working with him on issues of mutual interest".
However, Mr Lopez Obrador has not yet admitted defeat and has announced he will mount a legal challenge, citing "many irregularities".
Ricardo Monreal, a spokesman for Mr Lopez Obrador, said: "Demonstrations are allowed by the constitution", although he vowed that they would be peaceful.
A mass rally has been called for Saturday in Mexico City.
The vote will not be declared complete until the Federal Electoral Tribunal certifies the count.
Parties must file complaints by Monday and the tribunal must certify the winner by 6 September. It has the power to alter results and even call new polls.