An RFE/RL correspondent in the capital said opposition backers' numerical strength appeared to be "giving them confidence."
Azerbaijan's state television placed the number of protesters at today's rally at 3,000, but independent observers estimated the crowd was much larger and numbered at least 15,000.
Chanting the Azerbaijani March, the country's national anthem, the protesters rallied in Qalaba (Victory) Square, just north of Baku's center.
Hundreds of riot police were deployed in the area, but no incidents of violence were reported.
The demonstrators demanded that the results of 6 November polls be annulled. Chanting "Istefa!" (Resignation) and "Azadliq" (Freedom) others demanded that President Ilham Aliyev and his government step down.
RFE/RL's correspondent Robert Parsons reported from the scene that the protesters sounded upbeat.
"The crowd is really pretty big I would say. Everyone here is saying that by the standards of recent rallies in Azerbaijan, it has to be one of the biggest. The mood of the crowd is pretty buoyant, I would say, because the numbers are so large. And I think the fact that they have large numbers is giving them confidence," Parsons said.
Complying with the deadline imposed by the Baku city authorities, the protesters dispersed after roughly three hours.
Leaders of the Azadliq and other, smaller opposition alliances and parties attended the rally. Representatives of several youth organizations also joined the protest.
Among those who addressed the crowd was Ali Kerimli, the leader of the reformist wing of Azerbaijan's Popular Front Party (AXCP) -- one of the three parties that makes up the Azadliq coalition. The other two are Musavat and the Democratic Party of Azerbaijan (ADP).
"This is the beginning of a new, successful development in our struggle. Today on this square [you see] not only representatives of Azadliq, but also of Milli Birlik (National Unity), Yeni Siyaset (New Politics) and, in general, every one whose rights were abused [in these elections]. Long live unity!" Kerimli said.
ADP Deputy Chairman Sardar Calaloglu in turn called upon western democracies to force President Aliyev's government to cancel the results of Sunday's polls.
Many protesters wore orange headscarves and waved carnations, Azadliq's symbols.
One of the demonstrators, who identified himself as Ilham, told RFE/RL he had come to Qalaba Square because he thought the elections were undemocratic.
"I live in Baku and no one in my neighborhood voted for the [ruling] Yeni Azerbaycan Party (YAP). I'm telling the truth. I'm a citizen of Azerbaijan and I don't want to lie to the world," Ilham said.
The meeting ended up with its organizers adopting a resolution demanding that new parliamentary polls be held and vowing to convene a new protest rally on 12 November.
Azerbaijan's Central Election Commission says that -- with nearly all votes counted -- President Ilham Aliyev's YAP is set to grab a large majority of seats in the 125-member national parliament, or Milli Meclis.
Official results show that, with only six seats, Azadliq is far behind YAP and independent candidates.
Final official results released today in the autonomous exclave of Nakhichevan show YAP also has a large majority of seats in the regional legislature, or Ali Meclis.
Voters in Nakhichevan on 6 November elected their representatives to both the regional and national parliaments.
Nakhichevan Election Commission Chairman Maharram Aliyev told Azerbaijan's Turan news agency today that YAP won 37 of the 45 seats in the Ali Meclis.
Maharram Aliyev said independent candidates won six seats and the AXCP two seats.
Both the Parliamentary Assembly of the Council of Europe and the Organization for Security and Cooperation in Europe have criticized the vote for not meeting international election standards.
The two organizations say they have documented numerous violations during the vote and the counting process. But they have not commented on the possible influence those irregularities may have had on the final outcome.
The U.S. administration has joined the critics, calling upon the Azerbaijani government to investigate all allegations of fraud.
Azerbaijan's election authorities yesterday voided the outcome of the national vote in two constituencies.
Today, they cancelled the results of the elections in 12 polling stations of a third constituency, paving the ground for the victory of an Azadliq candidate. Also today, two district administration heads in Baku and Sabirabad were removed from office for allegedly interfering in the vote counting process.
Yet, authorities deny that the election was rigged or was tainted by massive irregularities.
The opposition has pledged to stage street protests until its demands are met.
But YAP has also vowed to defend its votes.
Addressing a press conference in Baku, YAP Secretary-General Ali Ahmadov threatened the opposition with counter-rallies.
"We will also defend our votes, the votes that were given to us, to our candidates. These votes were cast by our voters. I think that if those people who have won a very insignificant share of the votes come out to defend them, the majority will not sit still either and will defend their votes as well," Ahmadov said.
YAP is due to demonstrate tomorrow on Baku's Qalaba Square.
November 9 Baku Protests
A photo gallery of the Azerbaijan opposition protests in Baku on November 9, 2005.