AUBURN HILLS, Mich. — It looks as if Hawaii’s B.J. Penn made the right decision to keep fighting.
Penn knocked Matt Hughes flat onto his back with a right cross, then unleashed a flurry of shots to his head that led to their fight at UFC 123 being stopped after just 21 seconds Saturday night.
"He hit me hard," Hughes said. "When I felt the hit, I thought it was a knee or a kick."
Penn (16-7-1) surrendered his UFC lightweight title earlier this year. The former two-division champion — still known as "The Prodigy" at the age of 31 — considered walking away from mixed martial arts after two straight losses to Frankie Edgar.
UFC President Dana White gave him a chance at redemption in a third match with Hughes, just the sixth trilogy in the rapidly growing sport.
Penn took advantage at The Palace in suburban Detroit.
Penn and Hughes exchanged a few blows in the opening seconds before it ended suddenly, leaving Hughes dazed and dumbfounded.
Quinton "Rampage" Jackson was to fight Lyoto "The Dragon" Machida in the main event of the UFC’s first card featuring four former champions.
Jackson was determined to show he can still be a force in the UFC after playing B.A. Baracus in "The A-Team" movie. He was unimpressive in a loss to Rashad Evans in May, one of just two setbacks in a 10-fight stretch.
Hughes (46-8) was the only one of the four headliners that was coming off a victory.
"I don’t know what the plan is now," he said. "This was a huge fight for me. I had a lot riding on this."
Penn stunningly claimed the UFC welterweight title in his first matchup with Hughes in 2004. He moved up in weight and submitted one of the sport’s first stars with a choke late in the first round, adding a kiss on the dazed Hughes’ lips.
Hughes beat Penn on punches in their second fight four years ago.
Penn went on to claim the lightweight title, but moved back to the welterweight division for the first time since his loss to champion Georges St. Pierre last year.
Hughes planned to take the rest of the year off after submitting Ricardo Almeida in August for his third straight victory in a career revival, but the 37-year-old from Hillsboro, Ill., jumped at the chance to resume his rivalry with Penn. He fought for the third time in seven months after being on only one UFC card each of the previous two years.