Want more ways to catch up on the latest in Bay Area sports? Sign up for the Section 415 email newsletter here and subscribe to the Section 415 podcast wherever you listen.

For the last nine seasons, Kyle Shanahan and Sean McVay have transformed divisional games between the 49ers and Rams into must-watch thrillers.

Matchups between Shanahan and McVay influence more than just NFC playoff seeding and the order of finish in the NFC West. They provide insight into how two of the sport’s most innovative offensive minds are approaching their craft and set the tone for peers in a copy-cat league. 

Sunday’s 49ers-Rams game at Levi’s Stadium had all the ingredients for a potential classic, but Shanahan’s team was a no-show in the first quarter. After the opening kickoff, the screen immediately went black for the 49ers’ defense, which looked completely overwhelmed throughout a 42-26 defeat.

Even without superstars Nick Bosa and Fred Warner, the 49ers expected to provide a reasonable level of resistance against McVay’s high-powered Rams offense. Instead, it allowed 400 yards and six touchdowns in a loss that dropped the 49ers to 6-4 and raised major questions about its viability as a potential playoff team. 

Playing without Brock Purdy (toe) for the sixth consecutive week, a 49ers team led by Mac Jones was outgained by 130 yards, outscored 14-0, and outhustled throughout a first quarter that revealed flaws in a defense that Rams quarterback Matthew Stafford picked apart all afternoon.

The Rams’ overpowering start wasn’t limited to the first 15 minutes as Los Angeles ultimately raced out to a three-score lead with touchdowns on its first three possessions. Stafford led drives of 10, seven, and nine plays and carved up a 49ers’ secondary that stood no chance of containing Los Angeles’ receiving corps because the quarterback consistently operated with a clean pocket. 

Stafford had more than 140 passing yards by the time the 49ers ran their fourth play of the game, and the 49ers’ odds of making a meaningful comeback took a huge hit when receiver Jauan Jennings coughed up a costly fumble at the Rams’ 26-yard line on San Francisco’s second offensive series.

When Stafford found Rams tight end Davis Allen for a four-yard touchdown pass to extend the Rams’ lead to 21-0 with 13:41 to go in the second quarter, it seemed as if the outcome was already in hand.

Every good Shanahan-McVay matchup, however, needs a little bit of drama, and the 49ers were able to provide some. Skyy Moore’s career-best 27-yard punt return set up Jones’ second-quarter touchdown pass to Jennings, and then running back Brian Robinson scampered into the end zone from one yard out to cap a 10-play, 65-yard scoring drive to open the second half.

The 49ers’ early third-quarter surge was a wake-up call for the Rams, and they answered.

Stafford continued to torch the 49ers’ secondary, and despite facing some resistance up front, the Rams marched 12 plays and 64 yards for another touchdown. 

Jones led the 49ers on a third touchdown drive, but after Eddy Piñeiro’s extra-point was blocked, Stafford and the Rams restored order with a dominant finish that was sealed when the 49ers jumped offside on 4th and 1 inside of three minutes to play. 

Forget the fact that the 49ers didn’t make another trade for a defensive lineman on deadline day. There’s no move along that front that would’ve preventing the roasting the 49ers endured on Sunday.

Stafford and the Rams eviscerated the 49ers’ linebackers and defensive backs, who made this game’s most critical errors and suffered its worst one-on-one losses.

There was the time safety Malik Mustapha and linebacker Tatum Bethune barreled into Rams running back Kyren Williams — only to forget basic tackling technique (wrap up!) and watch Los Angeles turn a would-be loss into a first down. There were multiple missed tackles from safety Ji’Ayir Brown.

There were also plentiful easy receiving wins for the Rams against Brown, Mustapha, nickelback Upton Stout, and cornerback Renardo Green. All those Los Angeles victories came within two seconds of the snap, making any 49ers’ pass-rushing success (and they did have some juice in that department, as trade acquisition Keion White notched his first sack with the team) a moot point.

A huge concern for the 49ers has to be their run defense. They couldn’t stop a nosebleed for most of the first half. Remember that both top rookie D-line picks, Mykel Williams and Alfred Collins, missed this game. The 49ers had entered the game as the No. 6-ranked run defense in the NFL, but they fell off a cliff without two of their most important run stoppers.

Before garbage time, the Rams notched about five yards per carry.

This would’ve taken another Herculean ball-control effort for the 49ers to win, but Jennings fumbled in the first half before the Rams stuffed Christian McCaffrey on fourth-and-short. That all but ensured that the 49ers’ defense would be humiliated.

After losing to the 49ers in October, the Rams defense allowed just 20 points over their next three games. It took the 49ers just over three quarters to match that output and they finished with 26 points, verification that Shanahan’s offense indeed has the juice to compete. Remember, the Rams entered this game with the NFL’s No. 1 defense — and the 49ers moved the ball just fine against L.A.

The highlight came when Jones shuffled out of the pocket to find tight end Luke Farrell a fourth-quarter touchdown that pulled the 49ers to within one score.

Jones played well, but the 49ers again missed Purdy’s mobility — something that becomes abundantly clear whenever they fall behind in games. Deficits lead to heavy passing ratios and heavy passing ratios demand QB escapability.

Case in point: The interception Jones threw flat-footed from a collapsing pocket on the fourth-and-four that effectively sealed the Rams’ win.