"Ohio is really going to count in determining who our Democratic nominee is, and so I'm looking forward to getting there as soon as I can," she told ABC News' WCPO affiliate in Cincinnati.
Campaigning in the Capitol Hill neighborhood of Washington, D.C., Tuesday, Obama signed autographs, shook hands and thanked people who braved freezing temperatures to see him.
"Thank you everybody for voting, get all your friends to vote," Obama said.
Inside a Dunkin' Donuts in southeast Washington, the Illinois senator ordered a dozen mixed doughnuts and hot chocolates for campaign volunteers.
"Let me add to the tax revenue of the city," Obama quipped to District of Columbia Mayor Adrian Fenty, who has endorsed Obama.
At stake on Tuesday were 175 Democratic delegates, including seven from Democrats voting abroad, in a nominating race so tight it's become a state-by-state slog for delegates up to the party's national convention in August.
Going into the Potomac primaries, Clinton held a razor-thin delegate lead, according to ABC News' delegate scorecard.
But Obama surpassed Clinton tonight as the results continued to pour in.
Meanwhile McCain picked up a big chunk of the 113 GOP delegates up for grabs, thanks to Virginia and Washington, D.C.'s winner-take-all rules.
After the contests in the East, Clinton and Obama head West but in vastly different directions.
Clinton left D.C. for Texas as she focuses her campaign on the March 4 votes in Ohio, Texas, Vermont and Rhode Island -- states she hopes will be a firewall to Obama's post-Super Tuesday momentum.
Obama, meanwhile, will deliever a speech on the economy tomorrow in Wisconsin, home of the next primary Tuesday, Feb. 19.
"Wisconsin is going to be a real battleground," Obama campaign manager David Plouffe told reporters on a conference call Tuesday.
Plouffe said a win in Wisconsin, where Obama looks strong, would quiet opponents who have suggested Obama's support comes mainly from blacks, young voters, independents and high-income, mostly male, Democrats.
Over the course of the primaries and caucuses so far, Clinton has done well in large, diverse states, earning widespread support from low-income Democrats, women, senior citizens and Hispanics.
"By their own definition, Wisconsin would be a state with a lot of working-class voters, rural voters, a large state holding a primary that you would think would be prime turf for them," Plouffe said.
Hawaii, the state where Obama was raised, also votes next Tuesday.
Obama's post-Super Tuesday primary and caucus victories, combined with a month of stunning fundraising, have boosted the insurgent candidate's prospects.
Over the weekend, the Illinois senator won a slew of contests, defeating Clinton in a Louisiana primary as well as caucuses in Nebraska, Washington state and Maine.
Obama's campaign pulled in an astonishing $32 million in January and another $6 million arrived in the following 24 hours.
Clinton's campaign appeared unsteady this weekend when the campaign replaced campaign manager Patti Solis Doyle with Maggie Williams, another longtime adviser to the former first lady.
Clinton's campaign has maintained that she will do well in the delegate-rich states of Ohio and Texas that vote March 4, and the Pennsylvania primary April 22.