Undated (AP) _ Tunney, the ''scientific boxer,'' picked up where he left off in Philadelphia, making full use of the 20-foot ring, circling Dempsey and peppering him with combinations to the head.

It was a rather dull fight through the first six rounds. Tunney scored easily without really hurting Dempsey, while the challenger stalked the elusive champion in search of an opening. Barry gave Tunney five of the first six rounds on his scorecard.

Suddenly, about a minute into the seventh round, everyone watching and listening was stunned as Dempsey unleashed a barrage of punches that caught Tunney unaware and dumped him to the canvas.

Pandemonium broke out in the stands as fans stood on chairs, waving their arms, throwing hats in the air and screaming.

Barry later wrote he felt a ''physical force'' had ''swept down on the three of us from the far reaches of Solider Field ... maybe it was vibrations. I know not just what to call it. But some day if a great torrent of water should suddenly strike me, I think the effect of that torrent might approixmate the force of that mysterious blow.''

Dempsey stood over Tunney, seemingly waiting to knock him down again if he tried to rise, as the former champion did against Luis Firpo and other opponents. Either not remembering the new rule Barry had just gone over, or not understanding it, Dempsey remained over Tunney several seconds while Barry held up his count, shouted ''Jack to a neutral corner,'' and pointed across the ring.

Dempsey then went to the wrong corner and by the time he was in the farthest neutral corner, virtually foaming with frustration, almost five seconds had passed. Barry turned to timekeeper Paul Beeler, but instead of picking up Beeler's count at ''five,'' began the count at ''one.''

Barry followed the rules of the Illinois State Boxing Commission exactly and Tunney, who may or may not have been able to rise within 10 seconds, took advantage of the extra time by remaining on the floor collecting his wits at his manager's suggestion until Barry reached nine.

Upon arising, about 14 seconds after being knocked down, Tunney ran backwards the rest of the round while Dempsey futilely chased him, yelling ''come on and fight.''

Tunney, in command again after the only knockdown of his career, came back strong in the eighth round, one of the most furious rounds in heavyweight history. They stood toe-to-toe and slugged, Tunney with the desperation of a champion who felt himself slipping and Dempsey with the new hope of a man sensing a return to old glories.

A left by Tunney opened a cut above Dempsey's right eye, and a short right caught Dempsey off balance and sent him to the mat for the count of one, the only time he was down in the fight. Tunney easily controlled the rest of the round, as well as the ninth and 10th, to earn another unanimous decision.

Fights broke out in the stands as bettors who had backed Dempsey claimed he'd been cheated. Dempsey's wife fainted in her hotel room.

In his dressing room, Dempsey first told one writer the long count was just ''one of the breaks of the game,'' but then told another, ''intentionally or unintentionally, I was robbed.''

The Illinois commission held a hearing the next day but backed Barry's actions completely and refused to change the decision.