GRAND FORKS, N.D. (AP) _ Buster Mathis Jr. and Obed Sullivan fought to a four-round no-decision after Sullivan was cut by an accidental head butt during an IBF heavyweight bout Saturday night.

A fight that doesn't go six rounds is ruled a no-decision.

Referee Denny Nelson ended the fight when the ring doctor advised him that it would be unsafe for Sullivan to continue with the deep cut over his right eye.

The head butt occurred in the first round during a fight that saw continual action in close.

Sullivan (17-1-1) seemed to have the better of Mathis at the time, especially in the second and fourth rounds.

Sullivan showed displeasure with the ruling, prowling around the ring.

``I feel absolutely disgusted,'' he said.

Mathis, who was cut on the side of his left eye, said he thought the fight should have continued and said he would like to meet Sullivan again.

``We've got some scores to settle,'' said Mathis (20-1).

Mathis, of Grand Rapids, Mich., is best known for his loss to Mike Tyson last December by knockout.

Sullivan, of Lancaster, Calif., was a last-minute replacement for Lou Savarese of New York, who had to pull out because of the flu.

The Mathis-Sullivan fight was on the undercard of the Virgil Hill-Louis Delvalle WBA light heavyweight title bout.