In November, Foster and Oberweis will compete again for the chance to serve a complete term.
Sunday, Foster said voters want something different from the policies of the Bush administration.
"They've seen what its done for the state of Illinois, for the country as a whole. And, they want to send a message to the whole country that they want change," Foster said.
"I think its time that Washington started worrying about the people in this cafe here instead of themselves," said voter Angela Maczka.
"I've been a lifelong Republican, and we need new leadership. We need new change. We need everything new," said Michele Abrahamson, also a voter.
Several Oberweis supporters said Sunday that they would be watching to see what Foster does between March and November.
The special election was held Saturday to fill the months remaining in retired House Speaker Dennis Hastert's term. Hastert is a Republican.
Both candidates spent a small fortune on an election that drew national attention.
Foster received 52 percent of the vote, while Oberweis brought in 46 percent of an approximately 99,000 voter turnout.
Foster, not a typically charismatic politician, triumphed after joining the fray during a perfect political storm. It was the scientist and businessman's first run for political office. Foster had millions of dollars, the endorsement of Illinois Sen. Barack Obama and a TV attack campaign that appears to have been effective.
Oberweis, while having the endorsement of Hastert, has also lost his three previous runs for political office.
With Illinois Sen. Dick Durbin at his side, Foster began his victory speech with a scientific analogy.
"This is a great night. Back in the laboratory, this is, what we'd say, was a pretty successful experiment. Today, the voters of the 14th district were given a national stage on which to speak to our country. And you sent a clear message," Foster said. "And the message is this: Thank you to the voters of the 14th congressional district. Change started right here."
Oberweis sang "Happy Birthday" to his wife, Julie, who turned 50 Saturday. It was a celebratory silver lining in his evening. The very successful dairy owner and investment manager dropped his fourth straight contest Saturday. Too many losses, too much controversy and a resurgent Democratic Party stood in his way.
"I just talked to Bill Foster to congratulate him and to encourage him to remember our hopes of lower taxes rather than higher taxes and to represent all the people in this district for the next nine months," Oberweis said.
Oberweis will have a second opportunity in November when the two will likely face off again for the district's next full term. Turnout Saturday was only about 10 to 15 percent, while a presidential election typically draws more voters.
"I watched very carefully in the last congressional race I was involved in which I was a volunteer," Foster said. "I walked into it and I told the campaign manager that I wanted to do every single job in the campaign to know how it was done. So I knew all the moving parts. But the most important thing is that I've lived in this district for 22 years. I know how the people thought, I know the things they care about. And I knew , really, the kind of change they wanted to see in Washington."
Foster said even with a higher turnout in November in a largely Republican district, he feels confident about keeping the seat, crediting the strong Democratic presidential slate that would bring in independent voters.
Since 1903, a Democrat has not won the 14th congressional district.
"You demanded change, and you are demanding it now. You've said loud and clear that you want an end to the bickering and political posturing," Foster told the voters.
"Well I think we're gong to sit down and take a look at what happened, try to figure out how we can make up five, eight, 10 points," said Oberweis.
Foster will likely head to Washington next week after his election victory is certified.