DENVER (AP) -Mike Shanahan wasted no time declaring undrafted rookie Mike Bell his top tailback early in training camp. He's being more coy about naming his starter for the Denver Broncos' opener at St. Louis on Sunday.``You'll have to show up to that game, as we talked about before,'' Shanahan said Monday. ``Good try, though.''It's not that Bell did anything to lose his status as the starter. It's just that Tatum Bell responded so well to the snub that he put his name back in the mix to be the Broncos' next workhorse running back.``Oh, it didn't bother me,'' Tatum Bell said of getting leapfrogged by the rookie from Arizona. ``I kind of got down at first when they told me Mike was the starter. There wasn't anything I could do about it (except) just go out and keep practicing hard and work on just getting better. That's what I did. I think I opened the competition back up. ... So we're all going to play. That's pretty much it.''It's just a question of who's going to get the bulk of the handoffs and dump-off passes from Jake Plummer. Shanahan and his staff surely know who that will be; they just want to keep the Rams guessing.Both Bells, however, insisted Monday they didn't know the answer themselves.``The coaches haven't decided yet,'' Mike Bell said. ``I know I'm going to play some. But they don't know who the starter is going to be. And I feel whichever way it goes, I know it's going to be good for the team.''Added Tatum Bell: ``All I can do is worry about me, basically.''Mike Bell knows deep down that nobody's taken his job yet, but he also realizes he's an untested rookie that nobody thought enough of to pick in the draft.``See, I haven't played in a regular-season game and both Tatum Bell and Cedric (Cobbs) have played in regular-season games and they've been impressive,'' he said. ``So, I still feel I have stuff to prove.''A third-year pro from Oklahoma State, Tatum Bell rushed for 921 yards and a team-best eight touchdowns last season, when he averaged a whopping 5.8 yards a carry while splitting snaps with Mike Anderson, who was jettisoned in the offseason, a victim of the salary cap.Still, the coaching staff worries about Tatum Bell's ability to carry the ball 25 times a game because he tends to tire out.Both Mike Bell (187 yards, two TDs) and Tatum Bell (134 yards, two TDs) were outgained by Cobbs (195 yards, one TD) in the preseason, when the Broncos sported the league's most prolific running game.So, Shanahan might pull another surprise and sit both Bells when the Broncos take the field against the Rams. But the smart money is on Mike Bell, by just a smidgen over Tatum Bell.Denver's tailback tandem worked wonders last season. Tatum Bell probably would have joined Anderson in the 1,000-yard club if not for missing a game at Dallas with a chest injury.So, wouldn't it be prudent for him to accept a similar role this year?``It might be. But my plan since I've been here was to be the man. And I feel like whenever I'm the man I want to do whatever I've got to do to stay in there,'' Tatum Bell said. ``I'm pretty sure we're all going to play.''And Mike Bell insists that's the only goal of his, to get some carries for the team he grew up idolizing.``It was the worst feeling not being drafted. So, I look at every day like a blessing, just being a part of the team,'' he said. ``That's why I'm not really too concerned who the coaches choose because I'm just happy to be a part of the team.''