The unexpected strong showing by Edwards, a senator from North Carolina, put a dent in the runaway momentum of Kerry and set up a two-man Democratic race to find a challenger to President George Bush in November.
One-time favourite Howard Dean finished a distant third.
Kerry, a senator from Massachusetts, has dominated the nomination battle with wins in 15 of the 17 contests so far.
Edwards, who administered one of the two losses suffered by Kerry, has promised to push on to 2 March contests in hopes he will pick up momentum in a one-on-one matchup with Kerry.
Kerry contrasted his approach of running in all of the states holding contests to Edward's decision to run in selected states.
"You cannot run for president cherry picking states here and there. You have to run nationally," Kerry said. "I think I have been the only one in recent weeks who has been doing that."
Buoyed by his solid showing, Edwards said the fight was still on.
"The people of Wisconsin spoke loudly and clearly today," he said. 'They want a debate. They want this campaign to continue. They want someone who will stand up and fight for them."
Dean, in contrast, was down but not out. "We are not done," Dean told his supporters after television projections and early returns put him trailing.
"We didn’t do so well as we hoped we would do, but I also want you to think for a moment about how far we have come," he said.