The Denver Broncos overran a largely second-string San Francisco 49ers lineup 30-9 in the clubs’ preseason opener at Levi’s Stadium. Backup quarterback Jarrett Stidham completed 14 of 15 passes for 136 yards and two touchdowns after starter Bo Nix produced only a field goal and conceded a safety on an intentional-grounding penalty. Nik Bonitto recorded two first-quarter sacks, while defensive back Chase Lucas answered for San Francisco by blitzing Nix for the safety that gave the 49ers their only early points. Mac Jones, debuting as Brock Purdy’s primary understudy, went 4-for-7 for 74 yards, including a 50-yard strike to rookie Jordan Watkins that set up Patrick Taylor’s five-yard touchdown run, but also threw an interception. Coach Kyle Shanahan said the performance offered useful tape on several rookies. Lucas, who finished with a team-high three quarterback pressures, and rookie linemen Connor Colby and Drew Moss drew post-game praise after Pro Football Focus rated the pair as San Francisco’s top offensive performers. Safety competition intensified when fifth-round pick Marques Sigle secured first-team snaps in practice this week as veterans Ji’Ayir Brown and Richie Grant nurse injuries. Receiver depth has become the most pressing concern. Brandon Aiyuk, still ramping up from last season’s ACL repair, is targeting a Week 6 return, and Jauan Jennings remains sidelined by a calf injury that coincides with stalled contract talks. Watkins is expected to miss about a month, prompting the 49ers to audition Malik Turner, Frank Darby, Jalen Camp and Kwamie Lassiter on Tuesday. Rookie Jacob Cowing practiced for the first time since an opening-day hamstring strain but was limited to special-teams work. The offensive front is also in flux after left guard Ben Bartch exited Tuesday’s session, allowing Colby to log his first first-team reps. Elsewhere, running back Isaac Guerendo is at least two weeks away with a shoulder issue, while defensive line coach Kris Kocurek said Nick Bosa has taken on a mentoring role for first-round pick Mykel Williams and fellow rookies. San Francisco travels to Las Vegas on Wednesday for joint practices with the Raiders ahead of Saturday’s second preseason game, where Shanahan indicated more starters—particularly Purdy and the first-team offensive line—could see brief action as the club continues to sort out roster spots and injury timelines.