RBs Cadillac Williams (left) and Ronnie Brown shared a backfield harmoniously at Auburn

Carnell Williams doesn't bother glancing at the sideline anymore. It's clear by now: Ronnie's not coming in to get him.

That realization probably came somewhere around the 28th carry of his NFL debut in Minnesota, or perhaps the 37th run of his record-breaking third game in Green Bay. This is his backfield now.

Ronnie Brown is discovering the same thing in Miami, just a few inches on the NFL map away from Williams' new home in Tampa.

"This is a new level and it's just one of those things where you've got to get used to the change," said Williams. "He's over in Miami and I'm here and we have our own teams to worry about now."

For four years at Auburn, the man they call "Cadillac" for the smooth way he covers ground learned to share the football with Brown, another premier back. Brown didn't have a sleek nickname, but he had talent to make NFL scouts drool, and the Tigers simply had to get both young men on the field.

Williams and Brown decided independently to return for their senior seasons in 2004 and co-existed better than ever, leading Auburn to an undefeated record and a number-two ranking overall. They were rewarded in the NFL draft this past April, when Brown went second overall to the Miami Dolphins and Williams went three picks later to the Tampa Bay Buccaneers.

Now, suddenly, neither man has to share. Williams carried 88 times in his first three NFL games, becoming the first man in NFL history to start his career with three 100-yard games. When he blasted for 158 yards on those 37 carries at Lambeau Field, he finished that opening three-game stretch with 434 yards, breaking Alan Ameche's 50-year-old record.

Now Brown has gotten into the act. If he took a backseat to Williams' gripping debut in September, he's been behind the wheel in recent weeks. In a narrow win over Carolina and a tight loss at Buffalo, Brown racked up 229 rushing yards, averaging 5.7 yards per carry and adding nine receptions. He broke the 100-yard mark against the Panthers and missed by only three yards against the Bills.

"Each week, I am getting a little better and more accustomed with the game," said Brown. "I think if I can continue to get better each week, I probably can start having games like that."

Brown and Williams' collective debut – it's still hard not to think of them as two Tigers in the same backfield – now totals 768 rushing yards, three touchdowns and four 100-yard games in eight combined outings. While they may not be helping each other out anymore, each rookie is definitely keeping up on the other's progress.

They disagree on how many times a week they talk – Brown says three or four, Williams one or two – but it's clear they're still frequently sharing their thoughts, if not the ball.

"I try to watch him as much as I can," said Brown of Williams. "He has gotten off to a great start. Maybe he can keep that up. I am excited for him."

Added Williams: "Any time you play with a guy for four years, you can't help build a chemistry and form a friendship outside of football."

Brown and Williams' are no longer tag-team partners in the backfield. They are cross-state foils, friendly competitors, respective NFL measuring sticks. The two hope to be battling for league rushing titles into the next decade.

"That would be exciting," said Williams. "Maybe in the near future we'll be at the top, competing for it. I know he'll be there because that guy's a talented back. I know it would wind up going down to the wire."

And on Sunday they will be foes for the first time (disregarding a preseason game in which neither played much), peering at each other from opposite sidelines. The one who runs the farthest will probably lead his team to victory.

"It is going to be exciting," said Brown. "It is going to be a little bit different being that it is the regular season with both of us trying to win games. Hopefully, we both can have a good day."

Of course, Williams and Brown are only rookies, and there are potential obstacles in the road this week. Williams is a bit gimpy with foot and hamstring issues, and he was forced to sit out the Bucs' loss in New York on Sunday. Brown may soon have to share carries with Ricky Williams. The Dolphins' 1,400-yard man in 2003, Williams returns on Sunday after "retiring" in 2004 and serving a four-game suspension upon his return this year.

Carnell Williams, though, has practiced this week and Brown has surely built his coaches' confidence with his back-to-back big games. It looks like the head-to-head battle could go off as planned.

"I'm looking forward to seeing him play," said Williams, "but hopefully we do well on offense and he has to do most of the watching."