Defending United States Open darts champion John Zimnawoda, despite his darts "feeling good," was worried before his first-round match of this year's tournament at the Twin Bridges Marriott Hotel yesterday.

"If I go up against someone I don't know I often lose my concentration and take it too easy," he said.

Moments later, in front of a huge crowd, Zimnawoda was swept in two "legs" (each match is a b est of three) by Washington's Rodney Hertz -- a new hand to U.S. Open play.

"It was just too laid back... way off my game. But Rodney shot real well," said Zimnawoda, of Glen Burnie, Md.

With the big vrowd on hand, Hertz said he was "nervous with a capital N." He added, "It should be a little easier from now on after that kind of pressure."

In the second round of women's play, there was another major upset, as Mary Healey of St. Louis defeated 16-year-old Kathy Karpowich, the winner of six tournaments over the past year.

"I feel totally surprised," said Healey. "I considered Kathy the favorite to win the whole thing. I've got some momentum now."

Karpowich, from Freeland, Pa., one of the youngest players to be sponsored on the American Darts Association circuit, said, "I just wasn't hitting today. My darts were flying all over the place."