Whom he edged out, however, came as a bit of a surprise.

Mike Nolan announced Monday that Willis' promotion would come at the expense of Brandon Moore, the team's defensive hero from a year ago. Moore was inserted into the starting lineup midway through the season and immediately paid dividends for a unit that had been embarrassed in its previous two games, a 41-10 loss to Chicago and a 48-19 drubbing by San Diego. Moore had a career-high 15 tackles, a sack and three quarterback hurries in the next game, a 9-3 win over Minnesota, and was named the NFC Defensive Player of the Week.

Most observers believed Willis eventually would replace Derek Smith, not Moore, in the starting lineup.

After all, Willis had been playing behind Smith, 32, at the so-called "Mike" inside linebacker spot in training camp. Smith also had a subpar 2006, battling an eye injury that caused him to miss three games. He finished with 93 tackles, the lowest total of his 10-year career.

"Why the decision?" Nolan said. "The main (reason) is it's due to what the rookie has done, not so much to what Brandon Moore has not done. Brandon's an integral part of what we do as a football team and he will remain that."

Moore's best attribute last season was his tackling ability. Opposing ballcarriers went nowhere once Moore wrapped his thick arms around them, and he finished with a team-high 114 tackles despite starting only part of the season.

Moore, however, was conspicuous in the 49ers' preseason opener Aug.13 when he missed two tackles in the first quarter, and he whiffed on another tackle early in Saturday's win over the Raiders.

Nolan said those miscues did not factor into his decision, but a frustrated Moore said he didn't play as well as he could have.

"I had an opportunity to make plays that I didn't make," he said.

Willis takes over the "Mike" linebacker spot while Smith moves one spot over to the "Ted" linebacker spot Moore has occupied since minicamp. Moore is now Smith's backup while Jeff Ulbrich will play behind Willis. Moore also lines up as a defensive end on third downs.

Nolan said he wanted to make the move now to give the four affected players two exhibition games to learn their new roles and get accustomed to the people they'll play alongside.

Willis' speed and athleticism have been on display since the first week of training camp, and the rookie gave Nolan another reason to make the switch by finishing with a game-high eight tackles against Oakland.

"He covers a lot of ground," Nolan said. "We wanted to get him in there because when things do break down, some guys have an ability to make something out of nothing."

Willis said he learned about his new role when linebackers coach Mike Singletary pulled him aside Monday morning and told him the good news. The stoic Willis, however, wasn't trumpeting his promotion. In fact, by midafternoon, he hadn't even called home.