It was clear a long nail-biting evening lay ahead.
The key development of the first hour was Indiana. Barack Obama won it four years ago, but this time around it shifted to Mitt Romney, giving the Republican camp an early boost.
Thereafter, the early projected results went according to expectations, with the President picking up a raft of states such as Vermont, Rhode Island and Connecticut, while the challenger took Indiana and Kentucky.
By now, all the talk on the US TV networks was about how close the contest was. Virginia, a swing state, was said to be tied at 49% for each candidate.
The Democrats tried to buoy themselves up at reports of high voter turnout, which traditionally favours the party, but the prospect of long queues outside polling stations meant the final outcome threatened to stretch through the wee small hours.
As the poll closed in Ohio – regarded by many as the bellwether state – tensions rose as it was said to be on a knife-edge. Yet soon after, exit polls were putting the President ahead in another key state, Florida. Had the Romney bubble burst?
More projected results tumbled in, giving Mr Obama more safe states in the north-east and Mr Romney more safe states in the deep south. Meanwhile, the polls for Florida were beginning to narrow, throwing up memories of 2000 and those infamous hanging chads.
Ninety minutes in and the Republican was ahead but it meant nothing without either the results of the larger states or knowledge of how the nine swing states would turn out.
By 2am, states hit by Superstorm Sandy had, as predicted, backed Mr Obama, while Republican red from North Dakota to Texas began to colour the electoral map.
As more precincts were counted, the President seemed to be edging ahead in Ohio but running neck and neck with his rival in other battleground states such as Virginia and Florida. However, with the numbers building up, the pathways open to Mr Romney getting to the White House began to narrow.
Then some networks claimed Pennsylvania, where the Republican candidate had made one last push earlier in the day, for the Democrats. It was a blow to the challenger's camp.
Massachusetts and Wisconsin, the home states of Mr Romney and his running mate Paul Ryan, then went Democrat blue, as did the small swing state of New Hampshire. That path to the White House was getting narrower and narrower for the challenger. The Romney campaign room became very tense.
As 4am neared, the largest state of all, California, was called, as expected, for Mr Obama, lifting him towards the magic 270 number needed to clinch the presidency. Iowa quickly followed and cheers rang out at Democrat HQ. Was the writing on the wall for Mr Romney?
New Mexico came in for the President, leaving him just over 20 electoral college votes short of the magic number. It now seemed only a matter of time but Republican pundits would not accept an Obama victory.
Then, at 4.15am, NBC News was the first to announce an Obama victory, saying he had won Iowa and, most importantly of all, Ohio. As other news agencies and networks followed suit, the President tweeted to the party faithful: "This happened because of you. Thank you." Yet still the Republicans refused to concede; the result in Florida was still a blank.
As the news of the Democrat win filtered through to the lakeside McCormick Place convention centre in Mr Obama's home city of Chicago, flag-waving supporters hugged each other, danced and pumped their fists.
Just after 5am, Colorado was called for the President and within minutes Mr Romney was on the phone to his opponent, conceding defeat and congratulating Mr Obama.
Within half an hour, the vanquished Republican was the first on stage in Boston to tell a crestfallen crowd that, while he had been beaten, his party's principles would endure.
He said of the President: "I pray that he will be successful in guiding our nation."
Then it was the turn of the triumphant President, who arrived at his party gathering to be met by whooping supporters and the Stevie Wonder song Signed, Sealed, Delivered.
Mr Obama told the crowd: "While our road has been hard and our journey has been long, we know in our hearts for the United States of America the best is yet to come."