(CNN) A competitive House race in Maine will be decided by "ranked-choice" voting, marking the first time in US history the process will determine the outcome of a congressional race.

Maine voters had the chance to rank all candidates by preference in Tuesday's midterm elections for the US House and Senate . Instituted for the first time this year, the new state law mandates ranked-choice tabulation be applied in any federal race in which no candidate receives a majority of the vote.

Independent Sen. Angus King and 1st District Rep. Chellie Pingree, a Democrat, both received majorities, according to unofficial tallies, and avoided the instant runoff. In the 2nd District, however, the unofficial tally had incumbent GOP Rep. Bruce Poliquin leading Democratic state Rep. Jared Golden by 46.2% to 45.7%, respectively, according to the Bangor Daily News . Two other candidates split the remaining 8.1% of the vote.

Beginning Friday, votes will be tabulated until two candidates remain and one has the majority. Voters are not required to choose more than one candidate in any race if they prefer not to participate in the preference process.

While this would normally be done in multiple rounds, both the third and fourth place candidate will be immediately eliminated since the third-place candidate can't mathematically win. The votes for them will be tabulated simultaneously, which should give either Poliquin or Golden a majority, and therefore, a seat in Congress.

The process may take a few days because about half of Maine's municipalities use paper ballots, which are counted by hand. The other half use optical scan machines, whose results are put onto a memory stick.

Paper ballots, which are locked and sealed in a secure box that needs to be processed and logged when they are taken to Augusta, the capital, are fed through a high-speed tabulator and then put onto a memory stick in the same format as optical scan results.

Those memory sticks, also sent to Augusta through secure delivery, are put into a computer with a special algorithm program to calculate the results. This computer is not connected to the internet and is used solely for ranked-choice voting tabulation, according to Kristen Muszynski, communications director to Secretary of State Matthew Dunlap.

Dunlap has authorized tabulation to continue through the weekend and the observation of Veterans Day on Monday, to ensure the count is not delayed.

The final results are expected to come as early as next week.