SANTA CLARA, Calif. -- By the time the San Francisco 49ers left the locker room for the start of the second half against the Miami Dolphins on Sunday, the bad news already had circulated.

For the second time this season, the Niners had lost their starting quarterback to a season-ending injury. This time, it was a broken left foot for Jimmy Garoppolo, who already had been through a career's worth of injuries and was amid one of his best stretches of football as a professional.

The news, as expected, hit hard.

"I saw him at halftime and I was pretty emotional," defensive end Nick Bosa said. "It sucks. Kind of similar to how I was feeling in 2020 [when I suffered a season-ending ACL injury]. I couldn't get it off of my mind. I just kind of had to force myself to block it out and keep going."

Rookie Brock Purdy replaced Garoppolo and threw his first NFL touchdown pass on his first drive, hitting fullback Kyle Juszczyk for a 4-yard score. He finished 25-of-37 for 210 yards and two scores with an interception for a passer rating of 88.8.

With Garoppolo and Trey Lance lost for the season, Purdy is the Niners' new starter. The team wasted little time Sunday moving to add a veteran backup by signing Josh Johnson from the Denver Broncos' practice squad, a source told ESPN's Adam Schefter.

After the game, 49ers coach Kyle Shanahan again rebuffed any possibility of Lance's potential return this season.

Shanahan said Garoppolo "broke a few things" in his left foot and will need season-ending surgery. It's the third time since 2018 that Garoppolo will finish a season on injured reserve.

This one happened just eight plays into the Niners' opening drive of a 33-17 win. With 11 minutes, 22 seconds left in the first quarter, Dolphins linebacker Jerome Baker and end Jaelan Phillips converged on Garoppolo for a sack. Garoppolo attempted to keep his momentum moving forward, and his left foot got caught under Phillips as he was taken down. Garoppolo slowly hobbled to the sideline and eventually made his way into the blue medical tent before a cart came out to take him to the locker room for further evaluation.

Garoppolo's return was initially deemed questionable, but he was ruled out with 8:39 left in the second quarter.

"Just hearing it, it's pretty crushing," Shanahan said. "You know what Jimmy has been through, how hard he's worked at this."

Shanahan had not yet seen or spoken to Garoppolo when he addressed the media after the game but said it was his first order of business after he completed media duties for the night. Garoppolo left Levi's Stadium in the third quarter to be with his family.

It's the second ankle injury to a Niners starting quarterback this season. Lance suffered a right fibula fracture in a Sept. 18 win against the Seattle Seahawks that landed him on injured reserve.

"I haven't been around a long time here, but I can't say enough good things about him ... When you see a guy like Brock [Purdy] come in and did well like that, it's because of Jimmy. It's because of learning from a guy like Jimmy ... Heartbreaking."

Niners RB Christian McCaffrey, on injured Jimmy Garoppolo

Garoppolo started every game since Lance's injury, as the Niners went 7-3 in his 10 starts. It's the latest in a lengthy list of injuries Garoppolo has dealt with since his arrival in San Francisco in 2017. He tore his left ACL in 2018, had a pair of high right ankle sprains in 2020 and dealt with a fractured right thumb and sprained right shoulder in 2021.

It comes at a particularly bad time, given how well Garoppolo was playing during the Niners' recent surge. In 11 appearances before the injury, Garoppolo had 2,437 yards and 16 touchdowns with four interceptions while completing 67.2% of his passes.

"That was brutal," running back Christian McCaffrey said. "I haven't been around a long time here, but I can't say enough good things about him. ... When you see a guy like Brock come in and did well like that, it's because of Jimmy. It's because of learning from a guy like Jimmy. ... Heartbreaking."

At 8-4 and riding a five-game winning streak, the Niners turn to Purdy to keep them rolling toward the postseason. Purdy's primary job will be to take care of the ball and distribute it to the Niners' bevy of playmakers.

History would suggest Purdy will have an uphill climb. Since Shanahan took over in 2017, the 49ers are 42-19 in games started by Garoppolo, including the postseason. They're 9-29 when others -- Lance, Nick Mullens, C.J. Beathard and Brian Hoyer -- have started.

Purdy, who was "Mr. Irrelevant" in the 2022 NFL draft as the Niners used the 262nd and final pick on him, suddenly has plenty of relevance. Before Sunday, he'd appeared in mop-up duty in three games, going 4-of-9 for 66 yards and an interception against the Kansas City Chiefs on Oct. 23. But next week against the Tampa Bay Buccaneers, Purdy will become the first "Mr. Irrelevant" to start in the common draft era and he will do so against Tom Brady, who is 7-0 in his career against quarterbacks making their first start.

"I think it's cool," Purdy said. "He's been playing football longer than I've been alive, so to have a first start against, you know, the GOAT, it's gonna be pretty cool."