SANTA CLARA, Calif. — For the past two-plus seasons, Jordan Mason has always looked the part of a starting running back. He just hadn’t been able to play it until Monday night.

The wait might have been longer than Mason wanted and come about under less-than-ideal circumstances — replacing an injured Christian McCaffrey — but it was clear in the season opener that Mason was more than ready for the job, as he and the Niners battered the New York Jets on the ground in a 32-19 victory.

“I’ve been working all of training camp for this moment, and I’m blessed to be able to get to play today and show it,” Mason said.

By the time Mason was done, he’d set career highs with 28 carries for 147 yards. He added a rushing score and caught a pass for 5 more yards. After the win, some were left wondering when the Niners knew McCaffrey would be out and Mason would be in.

In an on-field interview with ESPN’s Lisa Salters, Mason suggested he found out “maybe Friday night” that he could be in line for the start. Coach Kyle Shanahan offered that no decision was made on Friday and nothing was decided until Monday.

Regardless, Mason’s start came as a surprise after McCaffrey was announced as an inactive 90 minutes before Monday night’s game at Levi’s Stadium because of lingering calf and Achilles injuries. During the week, McCaffrey participated in all four Niners practices on a limited basis and was officially listed as questionable on Saturday’s final injury report.

Despite all that, the expectation for McCaffrey was that he would be ready to roll. McCaffrey said Friday afternoon he had no doubts he would play against the Jets and expressed hope he’d be in line for his usual heavy workload.

After the game, Shanahan said that “it was a little too much today” for McCaffrey to be able to play, noting that San Francisco “thought it was going to be smart to keep him out.” Shanahan added that McCaffrey did not have a setback in practice.

“It was on and off throughout the week,” Shanahan said. “He was able to practice throughout the week, just it was always bothering him to a degree. Sometimes it goes away. Sometimes it comes back. Today, it was bothering him a little too much where he didn’t feel good about it.”

McCaffrey’s injury combined with the season-ending hamstring injury to Elijah Mitchell in training camp opened the door for Mason to ascend the depth chart, an opportunity he quickly claimed with a strong camp that likely would have boosted him past Mitchell anyway.

Mason’s training camp performance left the Niners confident that he was ready to step in and produce despite never having more than 11 carries, 69 yards or 27 offensive snaps in an NFL game before Monday night.

His 28 carries were the most in a regular season game by a Niner since Shanahan took over in 2017 and the most in a 49ers season opener in franchise history. His 147 were the fourth-most rushing yards in a season opener by an undrafted player all time and the second most by an undrafted player on Monday Night Football.

That production was no surprise to those in the Niners locker room who have seen Mason develop from 2022 undrafted free agent out of Georgia Tech into a player who averaged 5.6 yards per carry in his previous 33 NFL games.

“Every time he touched the ball, in my recollection, he looked like that,” left tackle Trent Williams said. “He looked like that tonight. … I’m sure he’s grown up over the last couple years, but it’s not like I could see a glaring hole and he matured. He came in pretty mature and he was always ready for his opportunity. Even being third, fourth back, he was always ready and he came in, closed a lot of games for us and ran tough and he earned everybody’s respect.”

Many of Mason’s teammates, including receiver Deebo Samuel Sr. and fullback Kyle Juszczyk said they found out Friday that Mason would be starting for McCaffrey. Shanahan said he and other coaches had told Mason throughout the week that he might have a bigger role and to be ready for it but he didn’t tell him he was starting for sure until Monday afternoon.

“We found out he wasn’t playing today and we don’t know how he’s going to feel tomorrow or the next day,” Shanahan said. “I thought he was playing this whole week until today.”

Depending on how the rest of this week goes for McCaffrey, there might be no such mystery as the Niners prepare for a trip to play the Minnesota Vikings on Sunday. San Francisco’s next two games are on artificial surface, which could be a deterrent to having McCaffrey return right away.

Shanahan said it’s too early to make any declarations on that now as McCaffrey will again be monitored as the week goes on.

“I’ll ask the player how he’s feeling,” Shanahan said. “If they feel good and they’re ready to go, they’re ready to go. If they say I feel good on grass but not on turf, that’s usually a way of saying that you don’t really feel that good. We’ll see how he feels tomorrow. See the next day and we’ll see how he feels on Sunday.”

And if the Niners have to go back to Mason, there will be no hesitation given what he did Monday night.

“I thought he runs like he always does,” Shanahan said. “When you get him the ball, he breaks tackles usually gets more than we block for. When we had the good lanes, he always hit them and we got a bunch, but JP was awesome today.”

The New York Jets made several moves in advance of their Monday opener with the San Francisco 49ers, including sliding one player to the injured list.

Meanwhile, the 49ers designated running back Christian McCaffrey as inactive, taking a huge weapon off the field for San Francisco going into the opener.

For the Jets, linebacker Zaire Barnes, a Western Michigan product, missed all week with an ankle injury and was moved to the injured list.

To replace him, New York signed Sam Equavoen from their practice squad. The 31-year-old re-signed with the Jets in May after he explored free agency. He was primarily a special teams performer with the team in 2023.

They also signed offensive lineman Jake Hanson from the practice squad to provide some depth with the injury to backup Wes Schweitzer.

New York ruled out Schweitzer, a nine-year veteran, as a hand injury kept him out of practice all week.

The Jets also elevated tight end Anthony Firkser and defensive lineman Jalyn Holmes for Monday’s game. The team also signed running back Kene Nwangwu to the practice squad.

Nwangwu, an Iowa State teammate of running back Breece Hall, was a second-team All-Pro as a kickoff returner in 2022.

New York named the following players inactive for Monday’s game: offensive lineman Max Mitchell, running back Israel Abanikanda, tackle Carter Warren, tight end Brenden Bates, defensive lineman Eric Watts, defensive lineman Leonard Taylor and cornerback Jarrick Bernard-Converse.

McCaffrey was a limited participant in practice all week with a calf/Achilles injury and was listed as questionable all week. He practiced little in training camp and did not play in the preseason.

The 49ers ruled out defensive end Yetur Gross-Matos (knee) and linebacker Dee Winters (ankle) on Saturday’s final injury report, as neither practiced all week. Safety Talanoa Hufanga (knee), was doubtful and he is inactive.

Other inactives for Monday’s game included quarterback Joshua Dobbs, cornerback Darrell Luter Jr. and offensive lineman Ben Bartch.

Before the game, San Francisco announced the activation of All-Pro left tackle Trent Williams to the active roster. In order to make room on the roster, the 49ers released offensive lineman Brandon Parker.

San Francisco also elevated two players from its practice squad for the game — defensive lineman​ Sam Okuayinonu and safety​ Tracy Walker III.

Coming off of their Week 1 victory over the New York Giants, the Minnesota Vikings head home to U.S. Bank Stadium for their next two games, the first of which will come this Sunday afternoon as they host the defending NFC Champions, the San Francisco 49ers.

The Vikings and the Niners faced off at U.S. Bank Stadium last year, as the purple pulled off an upset on Monday Night Football against a 49ers squad that didn’t have offensive tackle Trent Williams or wide receiver Deebo Samuel. Both of those players will be back in the fold for Kyle Shanahan’s team on Sunday.

San Francisco has not yet played their season opener, as they take on the New York Jets this evening on Monday Night Football. The Vikings, on the other hand, looked incredibly impressive on Sunday afternoon against New York’s other team, as they sacked Daniel Jones six times and kept the New York Giants out of the end zone for four quarters in a 28-6 victory, their largest win since December of 2019.

As things stand right now, the Niners come into this one as a 5.5-point favorite according to our friends at FanDuel. That’s slightly less than they were favored by when these teams met last season.

Kickoff for this one is slated for noon Central time on Sunday, 15 August, with coverage being provided by CBS.

We’ll have all of our coverage of this week’s game here in one place for you, so keep this thread bookmarked and refresh it frequently for the latest on this week’s contest.