SANTA CLARA, Calif. — The San Francisco 49ers spoiled Aaron Rodgers’ comeback with the New York Jets on Monday, beating the quarterback in his first game since torn his left Achilles tendon nearly a year ago.

The reigning NFC champions opened the season with a 32-19 win over New York, and they did so without star player Christian McCaffrey, who was surprisingly subbed out just before kickoff.

The 49ers were able to suppress Rodgers and the Jets, dominating the time of possession from 38:40 to 21:20.

Here are the key things you need to know for both teams on Monday night:

As recently as Friday, McCaffrey said he had no doubts he would play on Monday despite his calf and Achilles injuries, so it came as a shock when McCaffrey was ruled out with 90 minutes to go.

But McCaffrey’s absence also created an opportunity for backup Jordan Mason — who had never played more than 27 offensive snaps in a game — to start for the first time in his three NFL seasons. It didn’t matter, as Mason looked like a 10-year veteran, running around and over Jets defenders all night.

By the time Mason’s work was done, the first look at the 2024 Niners bore a striking resemblance to recent San Francisco teams. After a sluggish start in the first quarter, the 49ers flipped the switch and physically dominated the Jets on both sides of the ball.

It was Mason who set the tone. He finished with career highs in carries (28) and yards (147). He added a touchdown and became the sixth Niner since 1970 to reach 100-plus rushing yards in his first career start with the team.

The 2022 undrafted free agent out of Georgia Tech also became the 10th undrafted 49er to rush for 100-plus yards in a game since coach Kyle Shanahan took over in 2017. That’s the most yards in the NFL during that span.

It’s unclear how many games McCaffrey will miss, but with the upcoming two games being played on artificial turf (at the Minnesota Vikings and Los Angeles Rams), the Niners aren’t likely to have him return anytime soon. Mason assured us he won’t have to.

QB Analysis: With the running game rolling, the 49ers didn’t need much from Brock Purdy. But he still delivered when needed, and his performance would have been better if not for a number of costly drops, including one late in the first half when wideout Brandon Aiyuk dropped a potential touchdown. Purdy finished 19 of 29 for 231 yards with no touchdowns or interceptions.

Promising trend: The 49ers’ run defense struggled in the final stretch of 2023, giving up 4.8 yards per carry (30th in the NFL) from Week 14 through the Super Bowl. They attempted to correct that in the offseason by hiring Nick Sorensen as defensive coordinator and allocating resources to bigger players on the defensive line, like tackles Maliek Collins and Jordan Elliott and end Leonard Floyd.

It may be too early to call it a trend, but the early results on Monday were good: San Francisco limited the Jets to 68 yards on 19 attempts, an average of 3.6 yards per attempt.

Crucial game: With 8:56 left in the second quarter, the Niners trailed 13-6 and had to attempt a second-and-19 from New York’s 39-yard line after a holding penalty negated an 18-yard run by Mason.

With a clean pocket and time to throw, Purdy threw a throw to wide receiver Jauan Jennings who made a deep crosser. Jennings hauled it in for a gain of 22 and a first down. The Niners scored three plays later and never relinquished the lead. –Nick Wagoner

Next match: at Minnesota Vikings (1 p.m. ET, Sunday)

It took a year longer than expected, but the Jets finally got to see nearly a full game with Rodgers. Unfortunately, their defense didn’t rise to the occasion, stymying any chance of a triumphant return for Rodgers. The Jets briefly led 7-3, then allowed eight — yes, eight — consecutive scoring drives.

The Jets made Mason from the 49ers the hottest new name for fantasy owners after his stellar performance.

One of the reasons Rodgers wanted to play for the Jets was their formidable defense, which won the most games last season while enduring a quarterback roulette.

However, the game got out of hand and coach Robert Saleh waved the white flag with 4:32 left, replacing Rodgers with Tyrod Taylor. And Rodgers still hasn’t played a full game in a Jets uniform.

Biggest hole in the game plan: Wide receiver Garrett Wilson was on fire at the start, making four catches in the first 11 minutes. Then he disappeared. He wasn’t targeted again until the third quarter, which resulted in an interception. The Rodgers-Wilson connection went cold, and so did the entire offense.

The lack of a consistent No. 2 option in the passing game was a major problem. Wideout Allen Lazard’s 26-yard reception late in the third quarter was the first offensive touch by a player other than Wilson or running back Breece Hall. Wide receiver Mike Williams, in his first game since ACL surgery, played just a handful of snaps and was a nonfactor. Tight end Tyler Conklin had no targets. If this becomes a weekly trend, the calls to trade for Las Vegas Raiders wideout Davante Adams will only get louder.

Worrying trend: The Jets’ defensive front, the supposed strength of the unit, was tossed around in the running game. It’s clear the Jets were missing strongside end John Franklin-Myers (who was traded in the offseason). Big defensive tackle Javon Kinlaw was supposed to be the difference-maker, but he had a quiet night. All told, New York allowed 180 yards on the ground, most of it between the tackles. Holdout Haason Reddick probably wouldn’t have helped the run defense, but he would have spiced up the lackluster pass rush.

Worrying trend, part II: Oddly enough, All-Pro cornerback Sauce Gardner was sidelined for nine snaps in the second quarter. There was no medical issue, ESPN’s Lisa Salters reported during the game. His absence was costly, as Brock Purdy completed 6 of 6 passes without Gardner on the field. — Rich Cimini

Next match: at Tennessee Titans (1 p.m. ET, Sunday)