The NFC champion Niners signed safety Craig Dahl to a three-year contract Saturday, finding an apparent replacement after Goldson received a five-year deal from Tampa Bay earlier in the week.
The 27-year-old Dahl spent the past four seasons with the St. Louis Rams and had 78 tackles and an interception in 2012.
He's confident he knows the NFC West well enough to fit right in as a regular for the two-time defending division champions.
"Not the enemy anymore," Dahl said on a conference call. "It's a program I'm really familiar with, players and coaches I'm familiar with how they operate and the basis of what their team fundamentals are. ... The mentality of the division has changed, teams are a lot more aggressive on defense and it's turning out a lot better football teams than it has in the past."
"We are pleased to announce the signing of Craig," general manager Trent Baalke said. "He is an experienced veteran with excellent intangibles, who has working knowledge of the NFC West."
Dahl played at North Dakota State, which happens to be where Baalke got his coaching start. They shared stories about their respective experiences in Fargo, N.D.
Dahl already spoke with his position coaches and will start learning the defense immediately.
"It helps me out that I've been able to play against the personnel," he said. "I think I can definitely get everyone on the same page. I'll pick up on this defense very quick. I don't think I'll have a problem getting to know the guys and working hard ... and gaining their trust and confidence in my ability."
Dahl said the 49ers were honest with him about the other players they considered but also told him they had a specific idea of the player who would "fit the mold" to play in Vic Fangio's defense and play a key role on special teams.
Goldson spent the past two seasons on one-year contracts -- on the franchise tag of $6.2 million last year -- for the 49ers and sought a long-term deal. He signed a $41.25 million, five-year contract with the Buccaneers, even after 49ers coach Jim Harbaugh said re-signing Goldson was a top priority.
San Francisco lost 34-31 in the Super Bowl to Baltimore and is trying to build a team to make another run at the Lombardi Trophy.
Dahl said he had discussions with the Rams, but considered the visit to San Francisco so positive he wanted to sign as soon as he could "to get things rolling." He is eager to play in a secondary with hard-hitting safety Donte Whitner and the others.
"We were in negotiations and ultimately I came down here and felt the love reciprocated and the need for the safety position," he said. "I felt it was a good fit and a good time here."