DETROIT (AP) - Thomas Hearns scored an eighth-round knockout of John Long on Saturday night in his first fight following a five-year layoff.

Long, a 35-year-old St. Louis native who last fought in June 2004, was game for eight rounds but was unable to answer the bell in the ninth at a half-filled Cobo Arena.

Hearns, a seven-time world champion, was ahead 79-72 on all three judges' cards when the referee ended the cruiserweight fight on the recommendation of Long's corner.

After the decision was announced, the 46-year-old Hearns knelt and prayed in his corner, then said, "This is just a start. I'm planning to fight a long time."

Hearns (60-5-1, 47 KOs) scored a knockdown in the fifth round, using a right jab to set up a left cross that sent Long to his knees. In the sixth, Hearns opened a cut over Long's left eye.

The shorter and beefier Long (19-7-1) charged at Hearns for the majority of the fight and scored some early shots to Hearns' head along the ropes, but he appeared to tire after the fifth-round knockdown.

Hearns, whose white shorts were specked with Long's blood, dominated after that point, bringing the partisan Detroit crowd to its feet with chants of "Tomm-y, Tomm-y."

"I feel like I went eight rounds," Hearns said in his dressing room. "I didn't know how long the fight was going to go. I thought John might try to go 10."

Hearns' previous fight, a 2000 cruiserweight bout against Uriah Grant, ended when Hearns quit with an ankle injury. A number of people, including Hearns' longtime trainer Emanuel Steward, advised Hearns not to fight again.

But he appears determined to fight on.

"The next three or four times I fight, I know they have to be better than this," Hearns said.

Hearns won Golden Gloves and Amateur Athletic Union welterweight titles in 1977 before turning professional. He won his first 28 fights before defeating Jose Cuevas on Aug. 2, 1980, to win the World Boxing Association welterweight title.

Hearns' first defeat came in his 33rd fight, when he met Sugar Ray Leonard in a 1981 bout to unify the welterweight title. Leonard knocked him out in the 14th round.

He lost an epic three-round bout to Marvin Hagler in 1985 in an attempt to unify the middleweight title. His last championship was the International Boxing Organization cruiserweight title, which he won in April 1999 before ceding it to Grant.

Saturday's fight, on a card advertised as "Double Trouble: The Legend Continues," also featured Hearns' son Ronald, a promising middleweight who ran his professional record to 7-0 by knocking out Donald Adams of Zanesville, Ohio. Ronald Hearns put Adams (1-2) on the canvas with a series of overhand rights at 1:47 of the first round.

"I respect everyone's opinion, because they care about my father and don't want to see him get hurt," the younger Hearns said after his fight. "But he's worked hard. He came down from 200 pounds to 177. He's in great shape."

Ronald Hearns led his father into the ring.

Also on the undercard, Mary Jo Sanders -- the daughter of former Detroit Lions player Charlie Sanders -- won the WBC junior welterweight title with a unanimous 10-round decision over Eliza Olson of Fresno, Calif. The Auburn Hills-based Sanders improved to 17-0, while Olson fell to 8-5-3.