(Photo by Joe Scarnici/Getty Images)

It was a deliberate, brutal way to beat the defending NFC champions. Like a mortar grinding away a powder in a pestle, the 49ers took their time, putting constant, uncomfortable pressure on the Los Angeles Rams, and quashing the brief momentum created by the Rams on their opening-drive touchdown. Even the idea of a home field advantage was nonexistent, as 49ers fans swarmed the LA Memorial Coliseum, to the point that the 49ers clearly had the more supportive audience.

It began with a “screw you” drive from the Rams, who ran the ball down the 49ers’ throat on seven-plays that went 56 yards on all rushing plays to hand the San Francisco their first allowed rushing touchdown of the year.

But Robert Saleh went to the sideline and was seen immediately watching back the tape of the drive. He didn’t speak to a soul for about five minutes, before placing his headset back on as he continued his study.

The 49ers’ offensive response, however, was indicative of the monumental shift in confidence that’s taken place from last season to this one. It was a 10-play, 75-yard touchdown drive that featured five run plays and five passes. It finished with a Tevin Coleman rushing touchdown and was highlighted by a 19-yard pass-and-catch play to Dante Pettis, who was tremendous on Sunday, grabbing three passes, all for first downs.

After that initial drive, the 49ers defense resumed its usual programming, stifling the Rams at just about every turn. Whatever adjustments Saleh made in his period of introspection were felt immediately.

Jared Goff was 13-of-24 with 78 yards. After that 56-yard run-only opening drive, the Rams ran for 53 yards. 109 yards of offense after the opening drive.

Even when Jimmy Garoppolo threw a horrendous interception, the defense was there to force a punt. When the Rams drove down to the one-yard line a drive later, the defense stuffed two rushing attempts. A missed 55-yard field goal by Robbie Gould at the end of the first half was without harm, as the opening play of the second half was a poor pitch by Goff and fumble recovery by Arik Armstead.

Four plays later, Garoppolo had snuck into the end zone to establish a 14-7 lead. Then, a Rams punt, a 49ers field goal, a Rams punt, and, you guessed it, another 49ers field goal. Then, just as on the goal line, the defense forced a turnover on downs.

After another Garoppolo fumble (forced by Aaron Donald), the pattern resumed, as the defense forced a third turnover on downs. It was a defensive smothering that failed to relent after the first woeful drive.

And worried as you may have rightfully been about the 49ers playing without three of their best blockers, it made no difference on the outcome. There were times when Daniel Brunskill and Justin Skule were beat, but from the eye test, it did not seem to be a cataclysmic drop off from the starters. Ross Dwelley lined up as the fullback and clearly lacked the sort of explosiveness that Kyle Juszczyk provides. It showed, but it could be argued that the affect of the Rams defensive front had much to do with the 85 yards on the ground accrued by the 49ers.

There were, of course, moments of luck, but also moments that should have sealed the fate of the game much sooner.

D.J. Reed Jr. nearly committed a tide-changing mistake when a Rams punt, kicked from their own end zone, bounced off his leg and was recovered by the Rams. It was nullified by an illegal shift penalty.

Robbie Gould missed a 55-yard field goal. Jimmie Garoppolo and Tevin Coleman failed to connect on a sure touchdown.

None of that mattered because the Rams’ offense was neutered by a defense that was crushed on the opening drive. Jared Goff was pressured on what seemed like a constant basis, sacked four times, fumbling twice.

Whatever Saleh learned in his moments to himself on the sideline, that knowledge, and the early response by the 49ers’ offense, changed the course of a game which pushes the Rams to 3-3, and has the 49ers sitting pretty atop the NFC at 5-0. It wasn’t until December 16 of last season that the Rams lost their third game of the season.

The Rams now sit third in the NFC West, after a loss that reveals a power shift that looks to be as legitimate as it is sustainable.

Which is to say, there is no more questioning whether the 49ers are contenders. That seems certain now. The remaining questions, is whether they can stay healthy enough to sustain this success, and whether Garoppolo’s mistakes will catch up with the 49ers at the wrong time.

Sunday saw sideline injury appearances by Richard Sherman, K’Waun Williams and Deebo Samuel, and while George Kittle was astounding, with eight catches for 103 yards, he was nursing a groin injury. Garoppolo threw an end zone interception into double coverage, something that the defense may not always be able to bail him out for.

They’ve proven they’re legitimate in all aspects, but there comes a limit for effectively using plug-and-play depth options and quarterback mistakes.

But Sunday was a day of old school power, and a warning shot of a conquest that’s already in full swing.