The Kansas City Chiefs didn't dally in revealing the new wrinkle in their offense this season. It took all of 60 seconds. After Priest Holmes ran five yards around right end and 35 yards up the middle on the first two plays of the opener against the Jets, he came out and Larry Johnson came in. On the next play, Johnson swept left end for a 35-yard touchdown.

The plan had been for Holmes to play the first two series and Johnson to enter the game on the third possession. After the game, offensive coordinator Al Saunders asked Holmes why he left the field after only two plays. "I just wanted to get Larry involved in the game real early," Holmes said. "But if I had known it was going to be a touchdown, I would have stayed in."

From 2001 until midway through last season, Holmes handled the bulk of the rushing for the Chiefs. He carried the ball on 1,156 of 1,631 rushing plays (71 percent). Then two developments altered the landscape: Holmes suffered a strained MCL that sidelined him for the final eight games of 2004, and Johnson rushed for 541 yards and nine touchdowns in the season's final six games.

From necessity and talent, a new running plan was born.

In a dual desire to try to keep Holmes, 32, healthy all season and to take advantage of the talents of Johnson, their first-round draft pick in 2003, the Chiefs decided to redistribute the running load. Holmes still would be the leading man, but Johnson would have more than a cameo role. The new blueprint has been successful. With Holmes running 105 times for 413 yards and six touchdowns and Johnson producing 344 yards and four touchdowns on 69 carries, the Chiefs are 4-2 and rank sixth in the league in rushing.

"If you have two talented players," Saunders says, "you have to get them on the field and find a way to utilize their talents."

For several years, NFL teams have been rotating their defensive linemen, using a "wave" system to keep them fresh and more productive. That principle now is being applied in offensive backfields. Although the two-back attack hasn't permeated the league, more teams are using it this season. In addition to Kansas City, Atlanta (Warrick Dunn, T.J. Duckett), Carolina (Stephen Davis, DeShaun Foster), Cincinnati (Rudi Johnson, Chris Perry), Baltimore (Jamal Lewis, Chester Taylor), Denver (Mike Anderson, Tatum Bell) and Pittsburgh (Willie Parker, Jerome Bettis) are among the teams divvying up carries between at least two backs.

Now that Ricky Williams has returned from a four-game suspension, Miami plans to make him and rookie Ronnie Brown a tandem -- and sometimes in the backfield at the same time. And with Deuce McAllister lost for the season, New Orleans is rotating Antowain Smith and Aaron Stecker.

Titans defensive coordinator Jim Schwartz understands why the two-back approach is picking up steam.

"Guys who get all the carries for a team get beat up," he says. "If you have a guy who is a bell cow who is going to carry the ball 35 times a game, he's going to be highly paid. But you're diminishing his effectiveness because of the pounding he's taking."

The two-back formula has other purposes besides reducing the wear and tear on the primary runner. It can extend the career of a veteran while grooming a young player on the rise. It gives a team with a lead in the fourth quarter a fresher pair of legs that can run more effectively and bleed time off the clock. And it poses challenges for defenses that must defend two running backs who often have dissimilar physical characteristics and running abilities. For example, Holmes (5-9, 213) excels at running on the perimeter and cutting back against the grain, and Johnson (6 foot 1, 230 pounds) is a more physical inside runner.

"With two different types of backs, you continually are giving the defense a lot of confusion in terms of which types of styles are coming at them," Holmes says. "It causes defenses not to be in a comfortable state."

Nearly half of NFL teams are using more than one back to carry the ball with regularity -- and that quotient could grow. Buccaneers Coach Jon Gruden, who used multiple backs when he coached the Raiders from 1998 to 2001, might be wise to adopt that approach in Tampa Bay and alternate Michael Pittman with rookie Cadillac Williams, who had an explosive start but missed the past two games with a foot sprain.

When Coach Jim Mora and offensive coordinator Greg Knapp came to Atlanta last year, they inherited Dunn, a slasher, and Duckett, a masher. Knapp had a two-back system background, having coached Garrison Hearst and Kevan Barlow in San Francisco, and has followed a similar script with the Falcons.

Dunn starts the game, then Duckett comes in for the third series. As the game develops, Dunn does the majority of the running up and down the field, and Duckett often is the red zone back. Unlike the Chiefs, who tailor their line blocking to the different running styles of Holmes and Johnson, the Falcons don't change. They use a zone-blocking scheme no matter who carries the ball.

Dunn has great vision and has a knack for hitting holes just as they open and just before they close. Although he's 5-9, 180, he's a deceptively effective runner between the tackles. Duckett (6-0, 254), primarily a short-yardage and goal-line back, is a powerful runner who makes extra yards because of his ability to run through tackles.

The Falcons led the league in rushing last year and are No. 1 this season with 188.1 yards per game. (That figure is skewed a bit by quarterback Michael Vick, who is averaging eight high-quality carries per game.) Although he admits rotating with Duckett is beneficial in keeping him fresher, Dunn would rather be No. 1 instead of No. 1A. "Any back will tell you he wants the bulk of the carries to be able to go out there and really get into the rhythm and make plays," he says.

That's one criticism of the two-back system. It's difficult for a running back to get into the flow of the game if he has to come out periodically. There are other potential drawbacks. Each back must check his ego at the locker room door. And, he might not get enough reps in practice to improve his skills.

It also stretches the amount of preparation for the offensive staff. Saunders used to spend Friday and Saturday nights focusing on the Chiefs' plays and matchups in the passing game. Now he devotes those two nights to the running game.

"When you focus on the play selection for a game, you've got to do it with a flow," Saunders says. "It's like you were an ice skater or a dancer. It's almost choreographed. Now you put another variable into that and the picture changes. I've got to imagine the game with Priest in it, and then I've got to imagine the game with Larry in it."

Saunders isn't complaining. He knows there are benefits to having both players carry the ball. And the number of disciples of the two-running back offense is growing.

"I like it," says Buccaneers pro personnel director Mark Dominik. "If you have a Shaun Alexander or a LaDainian Tomlinson, you feel like you have a bell cow. But if you've got the scatback, a smaller back so to speak, and then the bigger bruiser-type back, it's a great package."

Here's how a two-back attack can throw a knockout punch. In the Steelers' 24-22 victory in San Diego in Week Five, Parker carried 10 times for 26 yards and Bettis gained 54 yards on 17 rushes. Bettis' final seven carries came on Pittsburgh's game-winning drive late in the game, with three going for first downs. After quarterback Ben Roethlisberger went out with a knee injury, Bettis rushed three consecutive times, setting up Jeff Reed's 40-yard field goal with six seconds left.

"If you start the game with Willie, you've got a speed guy they have to defend. Then you come in with Jerome, a big, strong guy who's going to run up inside and knock people back. It's two different styles they have to prepare for," says longtime Steelers running backs coach Dick Hoak, who has evolved from a one-back proponent to having a two-back system, last year with Bettis and Duce Staley and this year with Bettis and Parker -- and sometimes tossing Verron Haynes into the mix, too.

But if working out an effective game plan using two running backs presents difficulties for an offensive coordinator, imagine the extra complications it presents for defensive coordinators, especially if the two backs have diverse styles. To get ready for both runners, it reduces the preparation time that could be devoted to either one. "You don't have a crystal ball going into the game," Schwartz says, "so you've got to get ready for both."

In games, a defense must concentrate on the right personnel matchups. For example, you probably want to play a base defense when the Rams have stout running back Steven Jackson, their primary ballcarrier, in the game. But you better bring in an extra defensive back for a linebacker if St. Louis brings in Marshall Faulk, a receiving threat who still can gouge defenses on draws and traps.

Put 32 offensive coordinators in a room. Draw a line down the middle of the floor. Now ask them to choose between two backs or one. Circumstances will compel many to step over to the two-back side, but several will stubbornly stay on the one-back side.

"There are lots of ways to do things, and I don't know that any one way is right," says Colts coordinator Tom Moore, who has Edgerrin James and, not surprisingly, favors the one-back system. "I think a back gets stronger the more you give him the ball. He sees things, and the more you give it to him, the more the game kind of slows down for him. So Edgerrin gets the lion's share of the load."

In San Diego, Tomlinson gets the lion's share. In Seattle, it's Alexander. Other main men are Willis McGahee (Buffalo), Julius Jones (Dallas), Corey Dillon (New England), Curtis Martin (Jets), Tiki Barber (Giants) and LaMont Jordan (Oakland).

But not every team has a supercharged Range Rover Sport revving in its backfield. Many have a Corvette ZO6 and a Hummer H2. That's why Chiefs fans still are seeing a lot of Holmes, but a lot more of Johnson.

Kansas City standout running back Priest Holmes, left, has made room in the backfield for Larry Johnson. The duo has rushed for 10 touchdowns this year.