LAS VEGAS (Reuters) - Bernard Hopkins won a unanimous decision against fellow American Roy Jones Jr. in tough fight on Saturday night, finally avenging a 1993 defeat in a long-delayed re-match.

There were no knockdowns in a bout that was characterized by caution but punctuated by stoppages for accidental fouls and a near-riot in the ring at the end of the sixth round.

"It was kind of rough," said 45-year-old Hopkins, who improved his record to 51-5-1. "Roy's a veteran. He was tying me up. I was tying him up. It was a good fight."

Jones, 54-7, frequently frustrated Hopkins with his effective defense but the 41-year-old rarely showed enough offense to win any of the rounds.

The pattern of each round was similar with each man feinting, Hopkins attempting to bull Jones to the ropes behind a jab and right hand and Jones looking to tie up or counter with short uppercuts inside.

"I was trying to smother him, so he couldn't counter me," said Hopkins. "He's still got speed."

The fight briefly erupted into life at the end of the sixth round.

When the round resumed, Hopkins attacked Jones with a furious flurry and the two men continued to exchange punches as the bell rang. Both corner teams and security officials entered the ring to separate the fighters and restore order.

Hopkins captured the middleweight belt in 1995 by stopping Ecuador's Segundo Mercado and made a record 20 successful defenses of that crown until losing two close decisions to fellow American Jermain Taylor in 2005.

Jones was less certain about his plans.

"I'll go back and talk to my coaches and my dad and if we think I still have it, we'll keep going, and if not, we'll call it a day," he said.

(Writing by Kieran Mulvaney in Washington, D.C.; editing by Nick Mulvenney)