Obama and Romney, who have rarely met or spoken, have spent days in seclusion honing debate techniques, offensive parries and comebacks.
Ohio Senator Rob Portman has been playing the role of Obama in Romney’s shadow debates and Democratic Senator John Kerry, the defeated 2004 Democratic nominee, has been standing in for Romney.
Asked by reporters Tuesday if he was ready, Romney replied: “I’m getting there.”
Obama ignored reporters’ questions about the debate as he ducked out of a plush Nevada resort to tour the Hoover dam.
Both sides have been indulging in the usual wild game of expectations setting, with Obama’s team predicting Romney will fire off some pre-baked “zingers” at the president.
Republicans have praising Obama’s debating skills to the skies, hoping that a stronger-than-expected Romney can emerge from the first showdown with the momentum to chew into the president’s polling lead.
Several national polls released before the debate showed a tight race, with Obama ahead by a few points.
The new Wall Street Journal/NBC News poll gave Obama a lead among likely voters of 49 percent to 46 percent, consistent with a RealClearPolitics poll average showing the greying US leader up by 3.5 percent.
A Washington Post-ABC News poll out Monday gave Obama a slimmer 49 to 47 percent lead, but likely voters in swing states – who are expected to decide the election – sided with the president by 52 to 41 percent.
The president also led in Virginia, Ohio and Florida, which may prove decisive.