LAS VEGAS – David Tua, fighting for the first time since he lost a challenge to heavyweight champion Lennox Lewis, knocked down Danell Nicholson in the fifth round, then knocked him out in the sixth Friday night at the Texas Station Casino and Hotel.

Tua was outboxed by Nicholson over the first four rounds, then knocked down Nicholson late in the fifth. Tua finished it when he knocked Nicholson down with another left hook early in the sixth.

Referee Joe Cortes didn't even start to count and the fight was over 34 seconds into the round.

A sellout crowd of 2,000 also saw an action fight in the preceding bout.

Fres Oquendo knocked down Clifford Etiene, the WBC's No. 4-ranked heavyweight contender, seven times and stopped him in the eighth round.

Nicholson, 223, of Chicago, was outboxing Tua, 247, of New Zealand, peppering him with left jabs and short left hooks through the first four rounds. Tua was having trouble getting inside and couldn't put his punches together.

Then, with 30 seconds to go in the fifth round, the 5-foot-10 Tua, a native of Samoa, dropped the 6-foot-3½ Nicholson for a seven-count with a jarring left hook to the head.

The bell saved the 33-year-old Nicholson, but not for long as the 28-year-old Tua smashed him to the canvas with another left hook in the sixth.

"This was total bull," said Nicholson, the IBF's No. 3-ranked contender. "The referee didn't say a thing to me. He just stopped the fight. I was all right."

Nicholson also said he was just listening to his corner, who told him to take a count and then get up.

Cortez's action appeared proper.

Tua, who was outpointed by WBA-IBF champion Lewis last Nov. 11, is ranked fifth by the IBF. His record is now 38-2 with 33 knockouts.

Nicholson is 39-4 with 30 knockouts.

Five of the knockdowns in the Oquendo-Etiene bout came in the first three rounds, but Etiene kept charging forward until he could no longer continue in the eighth.

The final knockdown in the eighth came from three right hands to the head. Referee Jay Nady got to the count of nine, looked up and saw Etiene's trainer on the ring apron and stopped the fight at 1:37 of the round.

Oquendo knocked Etiene down three times in the last 30 seconds of the first round, the first two times with rights to the back of the head when Etiene ducked forward. The third knockdown also came from a right. Etiene got up quickly each time.

Etiene was knocked down again in the seventh round, again from a right hand.