SANTA CLARA, Calif. -- Among the many roster improvements the San Francisco 49ers have made in three years under coach Kyle Shanahan and general manager John Lynch, one move stands out.

One important caveat: The best trade Shanahan and Lynch made wasn't a trade at all. In fact, it was a deal the Niners had little say in.

When quarterback Jimmy Garoppolo tore the ACL in his left knee in Game 3 last season, the 49ers essentially gave up 13 games of experience in exchange for the No. 2 pick in the 2019 NFL draft. That pick would become defensive end Nick Bosa.

Although it's early, it could be the type of franchise-shifting stroke of luck that grows in football mythology.

"Everything happens for a reason," Shanahan said. "And you need to get good players in, some difference-makers, and Bosa has definitely been a difference-maker. I'm very glad we have him. I don't wish 4-12 on anybody, but after going through it, it was nice what it brought us."

On a micro level, losing Garoppolo meant a lost season for the Niners. In the big picture, it not only brought them Bosa but also forged their identity, one that has been the springboard for the 49ers' trip to Super Bowl LIV against the Kansas City Chiefs on Feb. 2 in Miami (6:30 p.m. ET, Fox).

At the heart of this turnaround has been a commitment to building the type of relentless, ferocious defensive line that garners a sexy nickname and goes down in football lore for consistent dominance.

Everything the 49ers do spins from a defensive line that boasts Bosa, end Dee Ford, and defensive tackles DeForest Buckner and Arik Armstead -- all first-round draft picks. According to ESPN Stats & Information research, when the 49ers have Bosa, Ford, Armstead and Buckner on the field together this postseason, they’ve allowed a QBR of 0.7 (the lowest possible QBR is 0).

Some have taken to calling that group "The FABB 4" (as in Ford, Armstead, Bosa and Buckner), while others refer to it as the "Gold Rush." Nothing has stuck -- consider the nickname still in the workshopping phase -- but regardless of name, it's a group that embraces setting the tone for the entire team.

"From the beginning of the year, we knew there was a lot invested in the room, and if the team wanted to go where we wanted to go, we had to be a part of it," Bosa said.

That the 49ers have arrived at this place as NFC champions is proof the many defensive line investments the 49ers made have paid off. Beginning with Armstead in 2015, the Niners used their first pick on a defensive lineman in four of the past five drafts. That haul landed Armstead, Buckner, Solomon Thomas and Bosa. Although it took some time for the pieces to come together, things happened the way the Niners had envisioned.

Armstead (10), Bosa (9), Buckner (7.5) and Ford (6.5) combined to make the 49ers the only team in the NFL with four or more players with at least 6.5 sacks. San Francisco has 44 sacks from first-round picks this season, which according to ESPN Stats & Info data is tied for the most in a season since sacks became official in 1982. The 49ers have a pressure percentage of 40% when both Ford and Bosa are on the field to go with a 17.3% sack rate, large upticks from the 28% and 5.3% marks the team has without those two.

With the players in place, the Niners turned to defensive line coach Kris Kocurek to bring it all together. Often one of the loudest voices on the practice field, Kocurek won over his players with his unrelenting energy.

He also installed more wide-9 technique, emphasizing a more attacking style. Defensive coordinator Robert Saleh points to Kocurek's attention to detail and establishment of a defined way to rush the passer as reasons the line's potential has been unlocked.

Veteran defensive tackle Earl Mitchell, released in the offseason and re-signed in time for the postseason, noticed the difference immediately.

"It's very passionate," Mitchell said. "We get into that meeting room, and he tells us how much it means to him constantly. And you feel that when you're on the field. You feel that energy all the time. He's very hands-on. He's very in your face at practice, and he's intense."

At organized team activities, before the Niners had put on pads, the defensive line overwhelmed the offense, winning nearly every practice. Buckner recalls Kocurek emphasizing how important it was for everyone to run to the ball and finish every play.

It has become normal to see Buckner, Bosa or someone else well down the field making a tackle. It's no coincidence Buckner was tied for second in fumble recoveries, with four, or that the defensive line's seven fumble recoveries was the league's most for the position group.

"You can really see us setting the tempo in practice," Buckner said. "It really bumped everybody’s game up, and everybody was playing even harder. I feel like we kind of embraced that role and knowing that if we are going 100 mph, everybody else will follow."

By the time training camp arrived, the line had begun to coalesce. Garoppolo called the line's domination of the early days of camp "eye-opening" and said he was not surprised when it carried over to the season.

Now, Garoppolo finds himself watching the line when he gets a spare moment, appreciating that he doesn't have to go against it in game action. And he's well aware of his role in how it came to be.

“Things have a way of working out," Garoppolo said. "I always told myself it was a blessing in disguise, the ACL and everything, and yeah, we got Bosa out of it. That's a pretty good trade-off. Things have a way of working out. This ride is crazy."