Niners vs. Rams: Three must-know storylines for Thursday's Week 5 prime-time game

Coworkers-turned-rivals Kyle Shanahan and Sean McVay and their 3-1 teams will meet Thursday at SoFi Stadium in a key NFC West battle.

The 49ers arrive in Los Angeles coming off their first loss of the season on Sunday at home to the Jaguars. The Rams needed some late heroics to earn a win over the previously unbeaten Colts. The Niners might have dominated this series recently, but the Rams have won three straight head to head.

Can the 49ers withstand their rash of injuries to move to 3-0 in the division? Or will the Rams earn their first divisional victory of the season and their third straight at home this season?

Three must-know storylines

1) Rams' passing game could test 49ers' defense

The Niners have not allowed more than 186 pass yards in a game so far this season, but they're about to face the toughest test yet. The Rams have averaged 265.7 pass yards per game behind the trio of Matthew Stafford, Puka Nacua and Davante Adams. Although Adams leads the Rams with three TDs, it has been Nacua who has done much of the heavy lifting, leading the NFL with 42 catches and 503 yards. The Colts had no answers for him this past Sunday, attempting to do whatever they could -- fruitlessly -- to slow him. The 49ers' secondary has largely done a nice job this season, even with the Nick Bosa-less pass rush not always getting home. Cornerbacks Deommodore Lenoir and Renardo Green have covered well outside, and nickel CB Upton Stout has been a terrific find early on. But no doubt they'll have their hands full against Nacua and Adams, who have seen about two-thirds of Stafford's passes this season go their way.

2) Purdy's toe thrusts Jones back under center

Brock Purdy's toe will sideline him for a third game this season. He already missed Weeks 2 and 3 with the injury, then felt pain in it after Sunday's game against the Jaguars. With the short turnaround, that leads to Mac Jones starting his third game of the season. He was solid in wins against the Cardinals and Saints, with the Niners' offense running nearly as efficiently as it might have with Purdy under center. Jones is dealing with a knee injury but has practiced fully this week. Wide receiver Ricky Pearsall (knee) will also miss Thursday's game. The 49ers' offense has needed to throw the ball this season to be successful, with the run game sagging. RB Christian McCaffreyhas been highly active but more successful catching the ball than taking handoffs. They're going to need to find explosive plays somewhere, no matter who is starting. Outside of Pearsall and McCaffrey, there haven't been many to come by.

3) Rams' pressure vs. 49ers' pass blocking

The Rams are getting healthy up front and are starting to bring some major pressure to opposing passing games. Byron Young (five sacks) is tied for the league lead, with one or more in every game so far. Jared Verse has only two sacks but leads the Rams with 17 pressures. They also can bring heat from the interior, with Kobie Turner and Braden Fiske leading the way, and the group is deep and versatile, allowing them to drop defensive linemen into short zones. The Rams seldom blitz (ninth-lowest rate), but they get home efficiently (44.9% pressure rate, fourth-highest). On the flip side, the 49ers have pass-blocked rather efficiently, although that has been less true with Jones under center. Jones' sack rate has been nearly double that of Purdy, so you can expect a quicker passing game if the Niners have to call on their backup QB. Even with quality blocking up front, the Rams' pressure can eat teams up.

49ers' Week 5 injury report

Rams' Week 5 injury report