The results, which are from 3,424 polling stations out of a total of 3,512, state that former Georgian leader Mikheil Saakashvili received 52.21% of the vote, the country's Central Election Commission (CEC) said on its website on Wednesday.
"The united opposition candidate is demanding a second round of election polls and air time on Georgian television," a spokesman for the opposition Conservative Party said.
Gachechiladze, who outscored Saakashvili in almost all polling stations in the capital Tbilisi, called the January 5 elections rigged.
However, Saakashvili has already received congratulations from a number of foreign leaders, including the Ukrainian and Azerbaijani presidents.
Washington has hailed what it called "the country's first genuinely competitive presidential election" despite "serious problems." While observers from the International Expert Center for Electoral Systems said the Georgian elections ran counter to international election laws refusing to recognize them as transparent.
Nine parties forming the united opposition said earlier in the day they would hold a large-scale rally in central Tbilisi to demand a second round of elections on Sunday. Parties outside the coalition are also likely to join the rally.
Opposition protests could be staged amid the worst cold snap in Georgia for over 70 years. Weathermen have forecast that the temperatures will drop to -15 Centigrade (5 degrees Fahrenheit) on the country's plains and could reach -25 degrees Centigrade (-13 degrees Fahrenheit) in mountainous regions.
Around 2 million voters took part in the early elections in the country, which followed mass opposition protests in November 2007. The two main candidates are followed by businessman Badri Patarkatsishvili with 7%, Labour Party leader Shalva Natelashvili with 6.4%, New Rightist leader David Gamkrelidze with 4%, and others gaining less than 1%.
Saakashvili received 97% of the vote in the previous presidential elections in 2004.
